Lofty718

@mk1_man are you using 6m3 of gas per day for heating? this seems quite a lot.. how big is your house?

Never I repeat ever allow a builder or a builders plumber anywhere near your heating system install. The house needs a system boiler on PDHW and a proper mixing control for the UFH circuit Or design the radiators and UFH to all run at the same flow temperature which would be the ideal. I have the same size house as you with a 630 ecotec plus and thats more than doubly oversized. I range rated it down to 6kw and it still heats the house perfectly. If you get a Viessmann 200W boiler this will mitigate the need for an accurate heat loss calculation since it has such a good modulation ratio.

The setup he's changed to is identical to mine

How much insulation is under there? It looks like 40mm

In mine it's only UFH over tiles. The flow temperature of the UFH today at 4c is 32c, around 10c it will be 26c With weather comp the floor is usually less warm to the touch than a high temperature system, because the idea is to be constantly replacing the exact amount of heat lost from the building at the lowest attainable temperature Your Viessmann on weather comp with all the insulation you have will likely acheive some really low floor temperatures while keeping the house nice and warm. It will likely behave very differently to your current setup of having high temperature water running down to the UFH blending valve.

Do you have a radiator circuit too or is it fully UFH?

Balance the radiators to give more flow to the cooler rooms, second line of defence would be TRV's on the radiators On/off controls on a heat pump is a no no. You want it open loop and dumping low temperature heat into as much floorspace as often as posssible

Can you post some photos of the job? how often are you visiting the site and what is left to be done?

Hi James, people warned you in your other thread in March 2023 that this builder did not sound like a good one and the costs were insanse. You clearly did not listen to anyones advice and went ahead anyway. I even sent you a PM at the time because I was alarmed by your post. Building contracts are generally not worth the paper they are written on unless the builder is not operating via a limited company. He sounds like a VERY cheeky fella he's already charging you 660k to renovate and extend a maisonette and is adding all of these costs on top.

Tanking is a british standard for all wet areas but I do not beleive it is mandatory. Bathrooms were not tanked at all for years and many with normal plasterboard are still working well today. My friend works for a council doing plumbing work, they definitely wouldn't get him to tank the walls either everything is done the cheapest way possible.

Narrow, not a huge deal but with 100mm spacings you can probably run 2c lower flow temperature A lot of heat pump installers strive for a 100mm spacing when speccing ufh

I'm rather suprised that in a new build passivhaus the installers would of put in UFH pipes at 250mm centres

Never mind, I've been bitten in many areas too we can't have our eye on the ball on everything It almost happened to me too but I sensed the incompetency of the installer and decided to do some digging myself. The main issue here is not with you but the lack of training and knowledge of most heating engineers in the country. I think it's partly done on purpose though by the manufacturers of boilers. A low temperature heating system will last much longer than one blasting out 70c water and cycling constantly The guy that was about to install my system had the Vaillant logo on his van, but he had never installed Vaillant controls or wiring centres before, he puts them all in with nest's that don't modulate the boiler just turn on/off.

£2000 for only a design fee would be throwing money away, all it takes is a good engineer. I don't know what he would be charging that 2k for in a domestic property. Say he's on £350 a day that's 5 and a half days of 'work' to do something you can work out for yourself, I designed mine myself and supplied the bits, just paying labour for the installation of it. One zone per floor sounds reasonable, personally i'd probably go with one zone downstairs and one for upstairs. That's how it is in my house. @Adsibob you are in N.London right? I know of a very good engineer that is an expert on Viessmans. He would probably only do quite a large overhaul of the system and wouldn't be cheap

@JohnMo Are you sure your valve is sized correctly? it's very important to get the right KVS value(mine is 1.6). I researched and sized it myself and it spends a lot of time in the mid position so I know it is doing it's job. Look into valve authority it's very important that they are sized for the correct pressure loss/circuit size, esbe has an app that does it for you. It would be one esbe valve per zone. One valve can do multiple manifolds, in theory you could run the whole house off of one valve and one pump, which is why I said your system would of been cheaper this way. edit - I'm not 100% one valve can do mulitple manifolds, maybe someone more experienced could answer that with more certainty. -No mixers on manifold -No multiple thermostats -No actuators on manifold -Less pumps The esbe actuator you want is an ESBE ARA662 (I got one off ebay for 80 quid) then as mentioned above you would buy a seperate 3 way valve that is sized correctly for the KVS value of the circuit. The valve would be a VRG131 valve they come in about 80 different sizes so it's crucial the valve is sized correctly