ectoplasmosis Posted October 22 Posted October 22 (edited) What is the 'room stat'? Do you mean the Vaillant Sensocomfort controller? If yes, which weather-comp 'mode' is it set to (Active/Inactive/Expanded)? What type (K2, K3 etc) of rads do you have upstairs, and how big are they in relation to room sizes? You should have had a 'radiator schedule' document with these details as part of the install/commissioning process. You should not have to fit a TMV or auxiliary pump to your UFH circuit, providing the radiators have been properly specified. My house has UFH downstairs and rads on the upper 2x floors, no mixing valve, single flow temperature. Works perfectly, whole house stays at a constant 21.5C. Edited October 22 by ectoplasmosis 1
Post and beam Posted October 22 Author Posted October 22 1 hour ago, ectoplasmosis said: What is the 'room stat'? Do you mean the Vaillant Sensocomfort controller? If yes, which weather-comp 'mode' is it set to (Active/Inactive/Expanded)? Yes its the 720/3 senso comfort and its on 'active' if i remember correctly. Rads are K2 at the sizes specified. I dont believe these are the issue. Not an expert and happy to be proved wrong but they have no option to be controlled seperately and that is what i asked for and is in my unqualified opinion the issue.
ectoplasmosis Posted October 22 Posted October 22 (edited) 10 minutes ago, Post and beam said: Yes its the 720/3 senso comfort and its on 'active' if i remember correctly. Rads are K2 at the sizes specified. I dont believe these are the issue. Not an expert and happy to be proved wrong but they have no option to be controlled seperately and that is what i asked for and is in my unqualified opinion the issue. Why do you want them to be controlled separately? All this would do is decrease efficiency, and increase the risk of defrosting problems in winter due to lack of water volume. Your current setup, with open-loop and no TMV or secondary pump on the UFH, is best-practice for achieving best comfort and efficiency... providing that the emitters have been sized/specified correctly! From everything you've said, it sounds like the system is probably designed and installed well enough, but the radiator circuit has likely not been balanced/commissioned fully, causing the rooms with radiators to undershoot the target temps. I'd advise getting the installer to balance the whole system, then tweak the heat curve setting to achieve suitable flow temps which keep all rooms at their intended temps. I really wouldn't recommend installing any kind of zoning control, or thermostatic mixer on the UFH, this would only increase running costs. Edited October 22 by ectoplasmosis
HughF Posted October 22 Posted October 22 26 minutes ago, ectoplasmosis said: Why do you want them to be controlled separately? All this would do is decrease efficiency, and increase the risk of defrosting problems in winter due to lack of water volume. Your current setup, with open-loop and no TMV or secondary pump on the UFH, is best-practice for achieving best comfort and efficiency... providing that the emitters have been sized/specified correctly! From everything you've said, it sounds like the system is probably designed and installed well enough, but the radiator circuit has likely not been balanced/commissioned fully, causing the rooms with radiators to undershoot the target temps. I'd advise getting the installer to balance the whole system, then tweak the heat curve setting to achieve suitable flow temps which keep all rooms at their intended temps. I really wouldn't recommend installing any kind of zoning control, or thermostatic mixer on the UFH, this would only increase running costs. This is exactly what I'd be doing... I know it's not what you asked for, but it's the right way to run the system for maximum efficiency.
SimonD Posted October 22 Posted October 22 49 minutes ago, ectoplasmosis said: Your current setup, with open-loop and no TMV or secondary pump on the UFH, is best-practice for achieving best comfort and efficiency... providing that the emitters have been sized/specified correctly! From everything you've said, it sounds like the system is probably designed and installed well enough, but the radiator circuit has likely not been balanced/commissioned fully, causing the rooms with radiators to undershoot the target temps. I'd advise getting the installer to balance the whole system, then tweak the heat curve setting to achieve suitable flow temps which keep all rooms at their intended temps. I did ask... 23 hours ago, SimonD said: Have you not received a design from the installer? You probably have got the weather comp curve set too high and should have been told by your installer that it takes a while to set the system up properly. Has the installer arranged follow up visits to balance the system when it gets colder? What we really need to know is what mean water to air temperature difference the radiators have been specified to. That way we can tell if there needs to be a flow temperature differential between the radiators and ufh. In 2025, a 2 zone system with rads and ufh needs to have an electronic mixer to properly deal with weather and load compensation within the heatpump and both the zones.
SimonD Posted October 22 Posted October 22 58 minutes ago, ectoplasmosis said: Your current setup, with open-loop and no TMV or secondary pump on the UFH, is best-practice for achieving best comfort and efficiency... providing that the emitters have been sized/specified correctly! Not necessarily. The heat outputs curves of radiators versus ufh are different - rads are calculated to the power of 1.3 and ufh to either 1 or 1.1 so it depends on multiple design factors and the thermal properties of the building, including the balance of area between rads and ufh. Because this differential may often result in different flow rates, especially at higher mean water to air temperature differences, a mixer is used to offset this by adjusting flow temperatures to each zone.
Post and beam Posted October 23 Author Posted October 23 So if i installed a mixer and ran the radiators at a slightly higher temperature. How would the UFH behave? bearing in mind the gentle .4 WC curve remains (perhaps not) #A: down mix temperature to some value and run for as long as ... well how long actually? #B: Run at the same temperature as the radiators but for a short period. Currently the Delta T is 3 degrees so the down mix would be minimal would it not.
JohnMo Posted October 23 Posted October 23 1 hour ago, Post and beam said: Currently the Delta T is 3 degrees But think about this logically - if inside of house is 21, and you are flowing 25, 25 less 3 is 22. If your floor temp is 1 Deg above room temperature your dT cannot be any different. Your return temp cannot be lower than the floor temperature ever. But as asked previously are your room temps accepted and at target temperature upstairs now you are living in the house. Is this a question you seem to avoid for any reason or have you just missed the previous questions? 1
Post and beam Posted October 23 Author Posted October 23 3 minutes ago, JohnMo said: But as asked previously are your room temps accepted and at target temperature upstairs now you are living in the house. No. Apologies, appear to have missed responding to that.
Post and beam Posted October 23 Author Posted October 23 I only really mentioned the Delta T figure because the discussion usually mentions a 7 degree Delta T when the topic comes up.
Post and beam Posted October 23 Author Posted October 23 No they are not at the target temperature. And because i dont have seperate temperature control upstairs i wonder how it could be otherwise. Not withstanding that the radiators are the sizes specified by installer.
JohnMo Posted October 23 Posted October 23 Simple way is to flow higher temperature in weather compensation, but reduce floor output by reducing the flow through floor loops. On a day where you normally flow 25, increase flow to 26+ but increase dT across each loop (reduce flow) to 4+. Play with settings to get outputs of radiators where you need them while maintaining UFH output stable so as not to overheat downstairs.
HughF Posted October 23 Posted October 23 1 hour ago, Post and beam said: No they are not at the target temperature. And because i dont have seperate temperature control upstairs i wonder how it could be otherwise. Not withstanding that the radiators are the sizes specified by installer. Take the TRV heads off, turn the room stat right up. Leave it for a day.
ectoplasmosis Posted October 23 Posted October 23 (edited) 13 hours ago, Post and beam said: No they are not at the target temperature. And because i dont have seperate temperature control upstairs i wonder how it could be otherwise. Not withstanding that the radiators are the sizes specified by installer. As several have tried to suggest already: your best bet is to get the installer back to balance your system. It’s not that difficult to achieve. You don’t need to add or change anything right now. The system needs to be balanced and commissioned properly. Begin with this goal, and see how you go. Edited October 23 by ectoplasmosis 1
Dillsue Posted October 24 Posted October 24 19 hours ago, Post and beam said: Not withstanding that the radiators are the sizes specified by installer. What flow temperature did the installer size the rads for?
Post and beam Posted October 24 Author Posted October 24 3 hours ago, Dillsue said: What flow temperature did the installer size the rads for? 40c if i remember correctly. I always wanted no more than 35 if possible. Downstairs UFH is operating at below 30 currently
ectoplasmosis Posted October 24 Posted October 24 3 hours ago, Post and beam said: 40c if i remember correctly. I always wanted no more than 35 if possible. Downstairs UFH is operating at below 30 currently Your 40C flow design temperature will be met at the outdoor temp design temperature, i.e. depths of winter. All other times, the system will be modulating the flow temp based on the weather compensation curve. If you “always wanted no more than 35”, then you should have conveyed this to your installer and they would have sized the emitters for a 35C design temperature instead.
Dillsue Posted October 24 Posted October 24 4 hours ago, Post and beam said: 40c if i remember correctly. I always wanted no more than 35 if possible. Downstairs UFH is operating at below 30 currently So a 40 degree average rad temp probably needs a 43ish degree flow temp which is way more than you want to be running your UFH at. As others have said you'll need to throttle the flow through your UFH loops to run with the higher temp needed for the rads. If you're currently running your UFH below 30 you'll not be getting alot out of the rads
JohnMo Posted October 24 Posted October 24 On 16/10/2025 at 07:24, Post and beam said: But, because the thermostat gets to temperature 1 minute ago, Dillsue said: So a 40 degree average rad temp probably needs a 43ish degree flow temp which is way more than you want to be running your UFH at. As others have said you'll need to throttle the flow through your UFH loops to run with the higher temp needed for the rads. If you're currently running your UFH below 30 you'll not be getting alot out of the rads Issue is really one of commissioning and downstairs setup. @Post and beam is bouncing off a thermostat downstairs so heat doesn't get a chance to percolate through the house, running a lower flow temperature at warmer outside temps will help. Downstairs heat up rate reduces or ideally matches house heat losses, then everything has a chance to stabilise. Upstairs rads backfill where needed. If OP wants a two zone system. Installer will simply say I priced for the system you have and expect another £1k+ to make the changes. Will most likely need a buffer, electronic mixer additional pump and maybe additional controls. 1
JamesPa Posted October 24 Posted October 24 (edited) 16 minutes ago, JohnMo said: OP wants a two zone system. Installer will simply say I priced for the system you have and expect another £1k+ to make the changes. Will most likely need a buffer, electronic mixer additional pump and maybe additional controls. None of which will add any value and, if a buffer is fitted, will increase running costs. @Dillsue the advice others have given is sound. You don't need extra kit you just need to balance the kit you have and readjust the WC if necessary so you can operate comfortably with thermostats and trvs at max. You need to forget everything you were taught by manufacturers of add on controls about operating boiler based systems, it wasn't really true for boilers, and definitely isn't true for heat pumps. It needs a leap of faith but once done you should get a house that's much more comfortable than you ever will with a boiler and lots of fancy but irrelevant controls. Edited October 24 by JamesPa
SimonD Posted Saturday at 09:23 Posted Saturday at 09:23 20 hours ago, ectoplasmosis said: If you “always wanted no more than 35”, then you should have conveyed this to your installer and they would have sized the emitters for a 35C design temperature instead. 20 hours ago, JohnMo said: If OP wants a two zone system. Installer will simply say I priced for the system you have I think the main strand in the op is that @Post and beam asked the installer for 2 zones and 35c flow temp and didn't receive it. It's not @Post and beam' s fault, it's that of the system designer and installer because @Post and beam doesn't seem to know what he got. The designer and installer whether the same person or different people should have fully explained the plan so he knew what he was actually getting. (E.g. from a flow temp perspective, I can fully understand why you would choose 40C v 35C because the rad size difference there is significant). Unfortunately it is very common for designers and installers to do what they think/want to do with or without a customer's understanding. But then there are also too many idiots in the game that barely have half the required understanding and as a result cause these kinds of issues! (I know this very well as I've just had to explain manufacturer's installation requirements and MCS installation standards to a company operating an MCS umbrella scheme and didn't know what they were talking about!) All of this should have been conveyed by the installer in advance - discussed in depth with the op and confirmed a mutual understanding. As it wasn't they should be on the doorstep ready to get the system working properly!
Post and beam Posted Monday at 16:45 Author Posted Monday at 16:45 On 25/10/2025 at 10:23, SimonD said: think the main strand in the op is that @Post and beam asked the installer for 2 zones and 35c flow temp and didn't receive it. Exactly, and thank you. On 25/10/2025 at 10:23, SimonD said: If you “always wanted no more than 35”, then you should have conveyed this to your installer and they would have sized the emitters for a 35C design temperature instead. As per the above observation from @SimonD , i did indeed have many conversations with the installer,( and others that i rejected because of their responses). The entire point of this story is that i have not had what i have actually already paid for. Now, i take on board all the advice about tuning and optimising what i have. i am truly grateful and it might be that this gets me to where i have a balanced upstairs and downstairs. As an aside, i realised today that if i am operating in pure WC mode then the Hallway mounted room 'stat that i stressed so much about moving is in fact not relevant to my temperatures.
marshian Posted Monday at 22:59 Posted Monday at 22:59 On 25/10/2025 at 10:23, SimonD said: The designer and installer whether the same person or different people should have fully explained the plan so he knew what he was actually getting. (E.g. from a flow temp perspective, I can fully understand why you would choose 40C v 35C because the rad size difference there is significant). Oh yes sizing for 35 v 45 results in a significant increase in rad size as I found out On 25/10/2025 at 10:23, SimonD said: Unfortunately it is very common for designers and installers to do what they think/want to do with or without a customer's understanding. But then there are also too many idiots in the game that barely have half the required understanding and as a result cause these kinds of issues! (I know this very well as I've just had to explain manufacturer's installation requirements and MCS installation standards to a company operating an MCS umbrella scheme and didn't know what they were talking about!) I specified DHWP and WC on my boiler install and got S plan............ To give the installer credit he recitified the error and we got there eventually but fundamentally it was what he knew and he thought it would be fine.......... He also couldn't read a WC curve properly until I explained it... On 25/10/2025 at 10:23, SimonD said: All of this should have been conveyed by the installer in advance - discussed in depth with the op and confirmed a mutual understanding. As it wasn't they should be on the doorstep ready to get the system working properly! Trouble is installers talk a different language to customers - when you talk their language they don't always think you actually know what you want.
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