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Back in early 2024 I started looking at implementing UFH in (part of) our house. After watching this (and some of your other) videos at the time I decided to follow the advice here, and put in a CCT under the boiler, and add a 2nd pump for the rad circuit as a precaution against the problems described (in fact, the physical layout is almost identical to what you describe as "classic" CCT in another video). So far, it works well, although UFH warmup on very cold (-5 outside) days is slow, which I'm hoping is due to low-ish (60) flow temp setting (I'm about to implement weather compensation to try and alleviate this). Anyway, while the system is operating, I've been looking at the temperatures at various points, and noticed something interesting at the CCT. The flow temps are what you would expect (~60 or lower if the boiler has modulated down). The return temp *into* the CCT (from the converged UFH and rad returns) is also about what you would expect (flow -dt 20), but the return temp *from* the CCT into the boiler is almost at flow temp (maybe flow -dt 4?). Is this what you would expect? I can't help thinking that it needs some tuning. I notice the boiler (WB Greenstar 8000) has a setting to tell it there is an independent circulator, but it's not clear from the documentation what the intention of this is. There is also the possibility of adjusting the operating modes of all 3 pumps in the system (boiler, rad & UFH) if required. Any thoughts? Unfortunately I think I'm way too far North for you to come visit unless you fancy an all-expenses busman's holiday!

I have a 111 with a non-touch LCD screen and was wandering if it would invalidated the warranty with Viessmann if I were to install flat face unions instead of the supplied valves? Also where did you get yours from (I think the 111 flow/returns are 3/4")?

does having close coupled tee near the boiler negate the need to install automatic bypass on boiler which are setup in multi zone config?

Can the radiators ( 4 upstairs ) and water tank run off one side and the underfloor on when CH and HW off. So the radio are and tank both get 65C water then the underfloor goes the 40 the rest of the time ?

How do you get so much info on the display? Is this service mode? I have the vitodens 222W but cant reach that amount of info.

nice vid! do i need to turn off gas supply to replace these electrodes?

Hey I’m from Italy how do you turn it on? I just moved to a new apartment and they have one of these no idea how you turn it on it just puts on a red light “reset” that flashes can u explain to me how it should turn on?

Hi Andrew, I picked up on what you said about the pipe spacings at 200mm being too wide. I have one downstairs room with UFH, it has 16mm pipes at 250mm spacing. Does this mean that it could never be suitable for a heat pump, or are there some caveats to the bedrooms example you are referring to here? I’ve always found the floor too warm in this room (kitchen), but have just found the blending valve so have turned it down to 40 degrees from 55! Will have to see how that works out Octopus previously refused to install a heat pump for me, but they cited a ‘pressure drop’ caused by the UFH, and wouldn’t give me a detailed explanation

Useful video thanks. I am at the beginning of learning hydraulics really, having got so far with 'rule of thumb' basics. Can say a combi with a mix of UFH and rads ever operate satisfactorily without hydraulic separation, if say it only had one zone of UFH for one large room?

What’s diff between continuity and resistance?

Is short circuit no ohms?

Hi Andrew, Very helpful video, thanks for sharing. For underfloor mixed heating circuits on the 200-W do you modify the 934.5/935.5/936.5 "Differential temperature" setting from the default 8K? From my research I understand it takes the set flow temperature for the circuit and adds the differential, so for example a set flow temp of 22C it would add 8K=8C making it 30C. According to one document I've read "This enables the mixer to regulate more effectively and prevents it from being permanently open." Surely modifying the temperature higher by 8C will just waste energy by having to mix it down again? I would think having it set so the mixer remains near fully open would be more efficient by returning the cooler return water the boiler, so it modulates down quicker rather than diverting it to cool an over temperature flow. My system has an EM-M1 with ESBE mixer for the UFH and it usually sits around the mid towards closed position most of the time if just the UFH is on and has warmed up. The Viessmann 200-W manual does not explain this parameter very well and I may be way off base with this, but any comments or thoughts would be appreciated.

Hi Andrew, I’m in the process of installing a lowloss header for my system, which will serve radiators upstairs and underfloor heating downstairs in a standard semidetached house. The radiator zone will have only 4 radiators. My question is, will I need to install a secondary pump for the radiator circuit after the lowloss header? I’m concerned that while the boiler pump is powerful enough to circulate through the radiators, the presence of the lowloss header might result in short circuiting within the header itself. Would this prevent adequate flow to the radiators, thus necessitating a secondary pump?

I fitted weather comp and I cant get mine to ramp up to 80c when hot water is on it just stays at the central heating temp, i have got a tado fitted as well so it might be somert to do with that?

Not sure if a real problem, but whilst the relay is switching there will briefly be no resistor in circuit and maybe the boiler could determine a fault? Better to leave the 12k in place all the time and just switch a 1k1 across it (e.g. in parallel) using the relay.

Great video andrew, I have an Ideal logic combi and I wish to add weather comp but when I do it seems to fire the boiler permanently at full chat. I dont want to miss out on the benefits but do you have any ideas of how to fix this? I have a EPH CP4 controller installed on opentherm but the boiler doesn't seem to modulate at all.

Love the volumiser position. We wanted to do similar on a job but space didn’t allow it. We used a smaller model (still 25ltr) but vertical fit only.

What king a dude makes a video while chewing food. Good lord people are gross.

Cracking video Andrew I’d love to see longer videos of the install process, it’s such nice change to see all the components accessible and “serviceable” as supposed to slung in with no thought to how to work on in the future.

Fufking Hungry was you mate Jesus christ

Peice of artwork Andrew ❤ love the bends.

Nice and tidy. Is that in a modern house with insulation upto building regs?

Very pleasing to anyone. Would love to see technical detail. Even longer will be not be ignored by many.

Exciting times for heat pump installers... less so for the owners in 5 years plus when the components need access for maintenance or repair! There is ALOT to go wrong shoehorned into that cupboard 🤷🏻‍♂️

Nice job like always 👍

Hi, I work for Worcester Bosch. Our 5800i, 7001i and 3400 (split) all have access to our MM100 module which allows you to mix a heating circuit using a blending valve 👍🏻. We also sell ready made pump groups, but it is more cost effective to build your own with an MM100 paired with an additional circulating pump and blending valve (from someone like ESBE).

We're renting a ground floor apartment in a house that also has a separate 1st floor apartment. We have exactly the same boiler and control 470 fitted to it. The main PCB is identical too and we've got two cables running: 1 mains power to L (brown) N (blue) E (g/y) + another one to the same brown block with connected terminals AF (brown) and inner OT (blue). I didn't realise it's for the external sensor and assumed it's for a room thermostat. There are identical wires in a box in our lounge but they're currently connected to other old wires. I measured voltage thinking it's for the 24V room thermostat connection but there's no voltage on them (or 0.6V). I checked the boiler PCB that looks exactly like yours and 3+4 (red) are also short. It's a complex boiler but what I would like to achieve is to have at least one room thermostat in the house that's set to desired temperature so we could further control on radiators room temperatures between both apartments. We want tap water to be always available in the tank that's around 40 degrees Celsius (or at least on day-night schedule). We don't have any solars or recuperation installations - only single zone CH covering both apartments, HW and a tank that holds it hot + possibly the external sensor which I can't find anywhere because can't follow the AF + OT cable to the other end. We normally dial the CH knob all the way to the left to disable CH for summer and se it to anything over 30 or 40 for winter to reenable CH. The CH is currently also set on a 3 time slots schedule that's not enough as we have a gap mid night when it gets too cold (a missing fourth one would probably partially solve our issue). Also, often there are nights when it gets too hot in the flat when the CH switches on on the set schedule thus wasting GAS and money making temps uncomfortably hot in the house. Please note I have already purchased a brand new VRT 350 thermostat thinking it would allow to more control of temperatures using schedule as opposed to simple desired temperature dial. Do I need another room thermostat e.g. Vaillant VR81 Remote Control Unit 20129323 or/and additional VR61/4 two zone wiring centre for use with VRC470 20139853 (probably an overkill for a single zone) for the installation or just hook up the VRT 350 I already have directly to the boiler's PCB then set in Installation section room temp control to Thermostat in order to be able to control CH in one apartment's room and where would I need to connect it = BUS + / - next to 7 and 8 or 4 and 4 thus replacing the existing red short wire (am presuming polarity doesn't matter although no voltage is currently present in both)? How would it work with the external sensor if it's installed as well and which would override the other in what situations? EDIT - FOUND THIS USEFUL DIAGRAM - 7+8+9 are 24V connectors that should control my new VRT 350 wired thermostat. 3 4 5 are 230V and not suitable for VRT 350. community . tado . com/en-gb/discussion/2883/installing-the-extension-kit-on-a-vaillant-ecotech-plus-831

Or you have the appliance on

Great vid Andrew. This came up on my feed just in time.

Hi Andrew, I just saw this old video of yours, as we're looking into MLCP for our heat pump jobs. Interesting comment about secondary returns: I recently heard that someone has experienced failures with MLCP on second returns, as the inner plastic layer blistered and the pipe became brittle. Have you heard of this? Also, what's the issue with copper in this situation?

Hi , Andre what is the par number for the new model you use ,thank you

Great idea with those shims. I was hoping to install my HP on the existing 900 mm wide concrete footpath. It has approx 2 degree fall. Do you think these kinds of shims could work to correct that much?

Hi Andrew, thank you for the explanations and help. If you had a primary boiler loop with one CCT. Is it ok the run a pump from the secondary circuit for a radiator circuit and the pump on a ufh manifold to run that circuit. With this is it necessary to include zone valves for each circuit as they are separated from the boiler pump. Thanks

Well explained andrew ps i cant download app from link on esbe site it says link not found can anybody help?

Thanks for the teachings! Helping me a lot with getting my head around design.

Any simplification in using a 4 port mixing valve like the viessmann undermount mixers have. i.e do they automatically control authority. Happy to be completely wrong.

Hi Andrew, great video. Currently going through Heat Geek and this is really helping so thank you. What’s the difference between a low loss header and a distribution header and what application would require one over the other. Hope that question makes sense. Thanks very much again.

Where are you ordering the esbe valves from? I was getting them from that german company on ebay but service was shocking the more i used them. Price was on point though.

Very helpful, thank you

IMI Hytools app is also very useful for pipe sizing to velocity I find. Definitely important to understand the longhand calculation forst though.

Thanks Andrew, really interested although im still slightly baffled by the mathematics (muppettry on my part)One query i have always had is regarding the stepping up in size from a distribution pipe to another. For example, you mentioned using a 35mm section being fed by 28mm port, i have always assumed the 28mm will only pass a maximum amount of fluid/heat through so therefore query the usefulness of the 35mm section. Perhaps you can direct me to where I can study the fundamentals of that ? Many thanks, John

Very interesting, thanks Andrew. Hope you are well 👍

Very informative video once again Andrew! I was confused at the start of the video as im used to using the velocity triangle to work out flow rates for fixed quanity of water through a fixed diameter of pipe ie Quanity over area x velocity but understand your equation converts from M2 to mm instead of converting it yourself.

Lots of content coming through Andrew thanks !

Thanks Andrew !

That helps so much andrew thankyou. Heard you mention this app a few times and so glad as you've made this easy from now on. Thanks again

How did you learn this low loss header tank is there a course

Excellent video, i understood the principle but its nice to see exactly what part of the valve this applies to, whether is the bore size or the rotating port as you've shown. Also if its a complete sized valve required or different inserts to fit inside of a body. It looks like the whole part is what you purchase is it? Is the brass part esbe too or just the motor black box?

Is it still possible to get the mixers with correct kv/kvs in a neat thermal jacket like the meiflow ones were. If this is a domestic set up, what's the kvs on these valves as an example.

Looks a good setup. Out of interest would this arrangement work on a single pipe system? Thanks