HOW TO DRAIN YOUR HEATING SYSTEM - Pressurised - PLUMBING TIPS
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- เผยแพร่เมื่อ 6 ก.พ. 2025
- This video covers the basics of draining down your heating system to fix leaks, change radiators and move boilers etc. It covers isolating the water supply, venting the system, how to find your drain offs and radiator drop down legs, re filling the system, venting of air and inhibiting.
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This switch here turns it off, alright? That's the heating system off. We don't want it coming on or anything like that while we're draining down. The last thing we want is the boiler lighting up, or the pump coming on. It could burn the pump out, it could overheat the boiler and crack the sections. So the first thing you do is make sure that the heating system is switched off. "Ah, but James," I hear you ask in your stupid voice. "How does that pressurised heating system work?" "Well, y'know, I need a basic knowledge of them to know how to drain one down." Well, usually, you've got your boiler, your pump, any valves: you could either have a three-port valve there or a couple of two-ports. In this system, we've got two two-port valves.
Then you're going have your coil going into your cylinder, if you've got one; if not, a combi system. Then also you're going have your radiators, blah, back to the boiler, blah, back to the boiler. Now, some heating systems use a gravity feed in the loft to actually push water down, via gravity, from a tank up there with a ball valve in it down into the system. But nah, we don't have that on a pressurised system. 'Cos we ledges, aren't we? Yeah. Basically we have a cold water main come in, comes in, goes through a filling loop into what we call the manifold that's often at the bottom of the expansion vessel, So we've a big expansion vessel like that. So you got that, filling loop, braided hose. You have a non-return valve there, a valve there. This braided hose is removable, so the system doesn't automatically or accidentally fill up off the cold water main, which could pressurise it, which could bulge radiators, which could cause your whole world to come falling down. So yeah, there we go. That's the basic gist of how they work.
The water heats up, expands into this expansion vessel. Like I said already, go to our video on pressurised systems. So, let's have a look at this system here. So here's the loft that we're looking at and the particular part we're going be taking notice of is that bit there. So here we are on the lines down of possibly, possibly the worst pressurised heating system install I've ever seen. Right, so, we've got our feed from the cold main here. That's this valve here, we've got our braided hose here, that's also got a little valve in it that you can't see, but it's just a little black-handled valve. Let's get round here and have a little look. Can you see that? There it is. Now that braided hose comes up here and through this, which is a non-return valve,
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Instablaster...
I’ve been following you for years. I’m not a plumber and don’t really do any work on my system but just love your videos and find myself watching them all the time. Learned a lot too.
Every vid you make me laugh its thanks to you our first house (which we gutted completely) got a nice new bathroom PLUMBED BY ME and hasnt leaked. Im not a plumber id never touched plumbing before in my life until i got this house so thank you
Thanks James. Hadn't done this before. Really useful. Straight to the point, no filler, and the light-hearted humorous delivery turned my caution into confidence. Good Job Mate!
"Blue Peter without the drugs". Brilliant! I find that putting inhibitor back in before refilling the system is easiest via unscrewing the top bleed valve in the towel radiator in the bathroom and pouring it in, certainly a lot easier than trying to get it into a radiator top corner bleed valve port. Refilling then helps the circulation of the inhibitor chemicals pretty quickly
Just had to come back to my favourite video you have ever made! Every time I drain a system I think of throwing it like you and shouting “be free” 6:20sec into the video! Awesome James keep up the videos and I love the way they have evolved over the years.
Just searched for a "how to" on this subject and chose your video. Perfect! I followed your highly entertaining but informative, step-by-step instructions and now all done without a hitch. Many thanks for sharing, all those years ago! 👍
Thanks, mate, that's a useful reminder of a job I haven't done in, oh, twenty years or something. I like your STYLEEEE! You'd love the house I'm working on just now (moved in a few weeks ago): it's been owned at some point by Captain Bodge in person, just EVERYTHING slightly buggered up. The radiator I'm about to replace is hanging on one support - whoever fitted it completely missed the second support, which is fitted to the wall but not under the radiator. To check where the pipes are going I pulled up a couple of floorboards, which had been lifted in the past and re-fitted with one-inch panel pins. Yeah. I mean, we've all done the odd bodge in a lifetime, right? 6pm, due home half an hour ago, local shops shut, Screwfix out of stock - do what you have to do and get off the premises, but this place is just systematically bodged from top to bottom. Still, it means I get to hone a few practical skills I'd half forgotten.
Excellent info. I’ve changed 2 rads after watching this got it right first time.
You legend.
brilliant, i knew most of the things but i still watched because it was so entertaining and so well explained !! awesome job, keep it up !
james you can also use the rad valves as taps to drain down if there is no drain offs installed. when working with a plumber before he showed me how to use the valves as taps to drain down, i found that a good way when the dodgy plumber who installed the work years ago forgot to install a drain off point. great videos though man they help alot as i am going to study my level 3 plumbing and heating dipmoma at college in September.
Very useful and the sense of humour went a long way lol. Thanks pal! I had to move a radiator alongside the same wall and how to empty/refill the pressurised system came in handy. Now i need to understand what does the non-thermostat valve do as it's leaking when I unscrew it to a certain length. Will be watching you other clips. :)
Wazir
It's so rare to see entertainment AND well conveyed information, thank you and keep up the good work!
+Bikerchris No worries mate!
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Solid run through on depressurizing and pressurizing a system. I appreciated the technical aspect of what bars a proper system should be at. I assume that is standard. I am tackling my first project of a radiator replacement this weekend. Anyway, salute from the States (Duluth, MN).
I have no plumbing to do what so every......I just watch this guy because he's hilarious 🤣
Oh Why could my teachers at school be like you! Sheer brilliance! (Okay, school was 50 years ago!!)
Currently Doing my Gas Acs Cat 3, And these videos are helping me out so much as its things like these the course doesn't really teach you, but i've been coming across a lot on placement, So thank you very much man!
Brilliant mate! I could listen to you all day!
unique and very interesting style.useful knowledge and easy to understand well done. the answer should be C first and then B. I mean not only cup of tea, It must be with some cake and biscuits as well.Bless you.👍
I don't have a pressurised heating system to drain down but started watching this video anyway as yours are always interesting. After a couple of minutes in I was captivated purely for the entertainment value.
Well done on making a relatively ordinary subject so entertaining. I even got involved in the multiple choice. You should be a professional comic. Keep up the great work!
Aaron c what was the issue in the end, and if you can remember?
Great vid but how do you get the water out of the pipes so you can solder a new joint?
Fantastic! Thanks from Virginia, USA.
Hi.. can I just ask, when do I need to close the motorised valves… before or after the re fill
Great tips that will enable me to carry out the checks and repairs that I feel confident enough to do whilst leaving, as you say, serious issues to the professionals. Many thanks, John
Top stuff Johnno!
Mate what pressure should be in the pressure release cylinder before I add the water top up please?
love the presentation style. cheers... Can I ask what might be a dumb question... why is the system all filled up and then you think about inhibitors.... should I not pour it in to a upstairs towel rail before filling up the system.... sorry if this is a stupid question.
I'm going to remove the bathroom radiator so I can plaster the wall .now can you give me some advice . Do I need to do something with the combi boiler first before I remove the radiator or do I wait till I've attached the radiator back in place then go to the boiler.
Much appreciated as I won't remove the radiator until I know for certain what I must do .
Great video, informative and hilarious. Would it be worth checking/recharging the red expansion vessel while the system is drained?
Hi great videos. I have a radiator in the loft on legs, would that drain itself as its higher? I have a combi boiler with no tanks or cws. Cheers
All you need is an Alan key for the isolation valve. Ended up stripping the screw nut with a flat head as it was too tight. Thanks for the video we very nearly flooded the house and was utterly confused why we could find the IV.
Hi. I added a new radiator to my pressurized system, but I didn't fully drain down the system. I closed all the rads and just drained the water in the pipes, cut into the pipework and installed a new rad and then refilled/pressurized the system (my system has automatic air release valves). Took no time at all. Why do you have to drain all the system, why not leave the rads filled ?
I live in a block of flats with a communal heating system, how do I drain the system in the other flats?
Brilliant video
How do you drain and refill underfloor heating in a system?
how do u know if the hot water expansion? inlet valves are 'off' as u say they "should always be anyway" ?
My 3 storey house has drain valves on all radiators on the bottom floor and I need to put new valves on a towel radiator in a top floor bathroom. We have an unvented system like the one in this video with the red & white tanks and the hot water cylinder. Which radiator should I use to drain the system please ?
Great video thanks mate, is this the same procedure as a air source heat pump boiler system? Thank you for your videos
I was told never to drain the system because the water in the system is best. I wanted to drain it because when the system shuts off, I hear the water draining back to the main system. I don't think it is supposed to do that. Its like it is in need of water but the pressure is showing ok but still dont think it should make sounds like that. Looking forward to your thoughts! Great video's, makes me laugh! You missed your calling!
I'd put the inhibitor in before refilling. The towel rail on that system is the ideal place to add inhibitor.
Hi,
Been learning lodes from your videos.
I have a system which has both a water tank in the loft and pressure cylinder and actuator valve.
This has left me slightly perplexed.
In anycase I have drained my rad system.
Can I still use the hot water with the rad system drained ?
Thanks
Can I ask you an unrelated question.my system setup is a modern boiler on the wall that feed hot water to the tank and filled it up with hot waterI have my waste pipe from the boiler a plastic pipe that goes straight into the waste pipe under the sink when I run water and then stop after a few seconds I hear a noise in the boiler like the water is going back in the boiler thanks for reading my question
Does it make a difference if the boiler is located in the attic? Cheers
Every youtube video: "don't do this if you don't know what you're doing"
me taking a youtube crash course on boiler and heating systems: "couple more videos I should be fully qualified"
Hi. Great vids and used on other issues. But, I need to re-do a pipe leg to a ground floor radiator as too short. How do you drain the pipes under the suspended floor boards of the ground floor if the drain valve is higher up by the rad? Cut into the pipe and catch as much water as possible? Is there anyway to siphon etc? Sorry, its a open vent gravity system.
You have changed a lot in 8 years .. for the better
Ha! Thanks…😎
Ok....seems very logical to me, or so I thought!
I need to install a replacement radiator downstairs which is slightly larger than the existing one, hence I need to extend the pipes.
Now, we have a conventional boiler with a hot water storage tank and an expansion tank in the loft.
Imagine then my confusion when I found the hot water tank in the airing cupboard with an expansion vessel above?.?
No signs of any pressure gauges, so I’m wondering which bloody system I have- pressurised or not....
It would appear a hybrid of the two?! And whether I’m ok to stain it down then refill as for conventional....
Thanks !
Great stuff. Question.. I need to install an external bleed valve. Is it possible to install one by closing all radiators so I don't drain the full system. I have mega flow system.
Question mate from this video. Are am hearing you right that the shut off valve in the braided cold water main feed hose that goes to the expansion tank should be left OFF, all the time?
Love the style of the video and the detail man. Great job.
Mate, you are absolutely hilarious. You would make an excellent teacher. I've subscribed.
Hi I had to put more pressure in the boiler, and I can not turn the water of completly, so i had to turn the main water of, I have a new isolating valve, I thin k the old one is kackered and doesnt turn of completly, how do you drain the water system so i can fit new one, can you do it by opening the radiator and draining it that way, as thats the way I get the pressure back down again
Informative video James but I'm a little puzzled .. shouldn't you add inhibitor to the system before recharging the whole system with water.?
Can you make a video on how to to do a mains chemical flush?
Hi it’s a Gr8 helping video thx
Have u got any Combe boiler installation video or conversion video?
A lot of older systems retain the vented boiler system while updating to an unvented cylinder for the hot water to taps. In this case the boiler is still fed from a feed and expansion tank in the loft and the coil in the indirect cylinder is still vented. The cylinder itself is pressure-fed from the mains via a pressure regulator and fills with water at 3 bar. A "Y" system (3 port valve) ot "S" system (2 off 2 port valves) still makes the split between tap hot water and the radiator circuit. Actually I prefer the vented heat store system where the cylider water is simply a heat reservior - this water never changes. It's heated indirectly by a coil from the boiler abd hot tap water comes from another indirect coil in the sylider. The beauty of this system is that the hot water to the taps is freshly from the mains (the unvented cyliner water could hang around for days before being drawn off at the taps) and it does not need an annual service and check of the safety trips and valves as does the unvented. Nice video.
+diymostthings Cheers dude. I've got the old tank in tank tech too. Miles better!
thanks for putting up this video. I followed everything you said and my house is lovely and warm once again. thank you.
+Brian Dobbin No worries Brian!
We live in a bungalow and the only drain off i can find is in the bottom of the hot press yet there are radiators lower than the hot press.. i have walked all the pipes. Any ideas?
Hi I want to say thanks for sharing such a value able knowledge and Guidance with us it is highly appreciated I learnt alot from you I am new in Gas Industry .I need little help can you please tell me if you have any video for Conventional Boiler system to combi system
Do you need to let the radiators cool down before draining/removal? If so, how long does it take?
Very entertaining, it didn't help me in the slightest with my problem but I still watched all the way through. My system looks nothing like that and I'm in an apartment so there's no upstairs. I'm still none the wiser on how to drain my system (I'm at 2.5 bar) but I was entertained
I think plumbing is very hard job I could never figure it out. All the good plumbers out there never got any credit for the hard work they done.
Before I drain system I close all radiator valves that I'm not working on so rads are hopefully still pressured if valves hold is this ok or do you recommend drain everything
Superbly done
Do this go the same for a gravity feed system mate? Are is it diffrent
Love it! another comically brilliant video! thanks
Hi there, Thanks for all your great videos. I have to change a thermostatic radiator valve and the system is an open vent system with a Worcester Greenstar Ri boiler connected to a hot water tank. Do you know if there would also be a pump, though I can't see one, and also please could you tell me how to drain and then refill the system. There is a small black tank in the loft for hot water. Thanks so much, and hope you can help
Great videos thanks a lot. Can I just ask, I have the same heating system as this video. I need to re pressurise my pressure vessel. DO i need to completely drain down my central heating system first?
Plumberparts, Best to put inhibitor in before refiling with water.
Not true, you need to test your work for any leaks before inhibitor is added, otherwise you you could be draining the system down again to rectify the problem.
How do change heating/water valve on vaillant combo boiler
Thank you
I have searched and cannot fond a drain off valve on any of my radiators it is a pressurized system.. any ideas
Morning! regarding this video - at 10.41 which rads should you vent out, downstairs or upstairs first ?
man can talk...
solidary working can do this.
Awesome video.
last month a plumber changed the diverter valve in my boiler and after he finished work he pressurised the system to 2 bar. since then my house radiator are not heating up properly. I checked the room thermostat, bleed up the radiator but still we aren't getting enough heat from the radiator. before that we used to have 1 bar pressure and all of the rads were heating properly. so I doubt that might be due to more than 1 bar pressure. any suggestion would be really grateful. thanks
Good job but you missed the pressurising of the pressure vessel diaphragm cos sometimes it may not be pumped up.
Thanks for the great entertainment! I have a Worcester Bosch Greensted 30si and I need to add inhibitor, no plumbed towel rad, and no rads with a bleed valve blanking cap, they are all built into the radiator panels. Drain down and refill/pressurise is easy but where can I add inhibitor? Best option seems to be to remove an upstairs rad and pour into the pipes? Or is there a place to fill on this particular boiler? Thanks.
Shut a radiator off, drain the rad, then add it to the top of the radiator using a hose and funnel. Turn on and vent, you're done!
Great videos. Always love to watch.
Cheers mate!
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Hi, can I still use my combi boiler for just hot water while the system is drained down ? The boiler (Worcester Bosch 30CDI) has isolating valves on the flow and return
complete novice here XD looking to learn
what is the white tank next to the red expansion vessel ?
is it just a secondary expansion vessel ?
I wonder if you have any video on how to service an old floor standing gravity boiler?
No mate as we're not allowed by UK law to tell you!
That gauge you showed us was upstairs, was it not? Surely the cold working pressure you want to achieve depends to some extent on where you measure it - it should be about 1/3 bar higher downstairs than up, should it not?
Yes, but that's in a world where systems have multiple gauges on different floors...something that isn't common in the UK...in fact I've never seen it.
plumberparts - I was thinking of a system like mine. I have a combi boiler on the ground floor, and the pressure gauge is on the boiler front panel, 2.8m below the highest point in my system, which is the air bleed on a towel rail. When the system is full and that bleed is open and nothing is leaking in or out, my gauge should read about 0.25 bar. Should not cold working pressure be expressed as so many bar above that minimum pressure, which is 0.0 bar for a gauge at the top of the house but might be 0.6 bar for a gauge in a boiler on the ground floor of a three storey building?
I only have one white expansion vessel in the airing cupboard and no gauge or braided house, and need to change a rad, how would i repressurise after the rad change?
"Let water gush all over next doors primroses or something like that" 🤣
You kind of skipped the bit about how to inhibit the system. Yes I know you have another video with that on with your handy pump... however I'm just a DIY person with no tools and a pressurized system. To get my inhibitor in, I turned off my boiler system, drained some water and then added it to the towel radiator which you can fully unscrew (just poured it into the towel radiator). Then closed all valves, refilled and re-pressurized. Was that an ok way to do it? Keep up the good work, I’m pretty much sorted with what I’ve got to now (apart from rebalancing upstairs radiators perhaps) but you’ve helped me a lot with all your vids!
Hi, what about the boiler? Mine is a Potterton condensing system boiler with isolating valves. Should I turn these to the off position before draining the system to protect the boiler and pump getting an airlock when draining the system?
Also, it replaced an old gravity fed system. Whoever fitted it had problems with the little header tank, so they replaced it with a sealed expansion tank. The system works OK with this second expansion tank plus the one in the system boiler. Is it a problem? Any tips if it remains?
hi plumberparts, I was thinking about when you put the two two port valves in the open position. Once you have done all the work and put everything back together do you have to put the two port valves back into the position they were in at first. thanks
+Sean Neville No, when powered up they motor themselves back to the automatic position.
Great thank you very much. I may be draining down our system soon because there maybe some of that sludge in the system so it needs a clean. Also will one tub of inhibitor be enough for 9 radiators.
+Sean Neville Yeah, one's fine.
brilliant video thanks so much
brilliant delivery
At which point do you close the motorised valves
is this the same for electric central heating systems ? ie: OSO
What if you have a combi boiler with a digital display to show how many bars?
I need to drain the cylinder down to replace the seal on the immersion as its leaking ever so slightly also on a pressurized system. Is this similar to the heating system for draining and repressurising but finding drain off cock on the cylinder.
Love the vids
can you show newer boiler, ie baxi's etc
ive a pressurized system that is half under floor (ground floor, 4 feeds) anf half rads (1st floor, 4 rads) the motorised switch &
valve for the underfloor is knackered, is there anything i should be aware of when draining?
Is draining a combi boiler the same James as the pressurised boiler?
Your are awesome, will you come to the USA to fix my boiler system?
Amazing Videos love your sense of Humour
+Altaf Sheikh Cheers dude!
Hi
Thanks for your detailed explanations in all your videos.
I have a question regarding the system in this house. What is the little red cylindrical thing near the power outlets? I have the exact same thing in my system. It looks like a pump but I think that my heater (a Vaillant EcoTec) has already one inside it.
Could you tell me what it is and what it does? Again, it's not the big expansion vessel. The other red cylindrical thing. You are standing next to it at 8:44.
Thanks!
Hi, is draining the heating off a megaflow the same as draining off a combi?
+Bathroom worx Roughly. But you need to check the re-charge instructions for a Megaflow and also hold a G3 ticket! PP!
nice one bruv. u know your stuff. u mind need us doing u a video or keeping your crib tidy lol
You deserve fame my friend :) Loved it :)
Cheers Rachel!
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Hi,i have bleed the radiator for first time and i may have release accidentaly around 1 liter of water along whit the water,is it true that now i have pay a lot of money in my facture to my house owner,ita a rented flat.
You're the man. Good video
You little fibber! That phone call was not from someone wanting a quote, it was from me asking you to stop singing. ;)
As always, a great vid.
Cheers mate!