A booboo may have been made

[Post and beam]

I have a recent 5kw Vaillant heat pump to UFH downstairs and radiators upstairs. One senso comfort wired thermostat in the hallway.  Now that the heating is on i find that the ground floor is lovely and cosy. But, because the thermostat gets to temperature the cooler upstairs never asks for heat for the radiators.  In all discussions with my heat pump supplier i said i wanted 2 zones but hoped to not need the radiators on. I cannot see a way to control them in my current configuration.  Am i missing something ?

[Roundtuit]

I have a separate thermostat for upstairs.  What have you got upstairs that should be 'calling for heat'? TRVs?

[JohnMo]

Just sounds like you need a little balancing done

 

If your UFH is getting to temp and radiators not, your curve for the UFH is too aggressive assuming you are mixing via an electronic mixer. If no mixer, slow the flow rates to each loop in the UFH so it outputs less. Knock 0.5l/m off each loop. Less radiators as they are.

 

What flow temperature do you have set are you running weather compensation or fixed flow temperature?

[Conor]

Turn flow rates of your ufh zones down a bit.

[Post and beam]

4 radiators only upstairs, each with a TRV. But the TRV will never become relevant if the warm water is not present at the valve.

 

35 degree flow nominal , yes WC via the north wall temp sensor

1 hour ago, Roundtuit said:

I have a separate thermostat for upstairs

Well that forms part of my conversation with my supplier. 2 zones would imply 2 devices of control would it not. I understand that the senso comfort thermostat (vr720/3 i think) can do multiple zones. So i was content when this was specified and fitted. Only has 1 zone configured and i cannot see how to add a zone.

[Nickfromwales]

17 minutes ago, Post and beam said:

4 radiators only upstairs, each with a TRV. But the TRV will never become relevant if the warm water is not present at the valve.

 

35 degree flow nominal , yes WC via the north wall temp sensor

Well that forms part of my conversation with my supplier. 2 zones would imply 2 devices of control would it not. I understand that the senso comfort thermostat (vr720/3 i think) can do multiple zones. So i was content when this was specified and fitted. Only has 1 zone configured and i cannot see how to add a zone.

TRV’s respond to room temp, not water temp? 

[Post and beam]

1 minute ago, Nickfromwales said:

TRV’s respond to room temp, not water temp? 

There you go, the Booboo might have been me misunderstanding how they worked. I assumed they just did a restricting job on the water flowing through.

 

I did screw down the flow valves on the UFH manifold to the hallway and the downstairs WC last night. The WC is really quite warm. I will check later this afternoon if its made any difference yet. Going for a wired thermostat may not have been the best idea me thinks.

 

Just to say we have not moved in yet but i have been getting ready to do so this weekend.

 

[JohnMo]

26 minutes ago, Post and beam said:

35 degree flow nominal

That's your issue your flow temperature is way to high for current outside temps and a new build house. Your floor output will be huge, your thermostat is controlling nothing else.

 

Now the counter intuitive bit. You need to dial back the temperature, on your curve. This will allow a slower more measured heat input and allow more time for the radiators to back fill any missing room temperature. Low and slow will allow heat to be absorbed the building. Allow system to run without any setbacks or off periods.

 

Your WC should look something like this for the UFH 15 OAT flow 25 and -3 OAT flow 35. This will allow the majority of the heat for the house to come from the floor and your radiators just ticking over. If the house is getting to warm dial back the -3 flow temp 0.5 of a degrees every 24 to 48 hrs.

 

If you do the above you can leave the UFH flow meters fully open and leave the ASHP to control flow and dT.

Edited Thursday at 08:35 by JohnMo

[Post and beam]

Thanks johnMo, i will give this a go

[sharpener]

1 hour ago, Post and beam said:

2 zones would imply 2 devices of control would it not. I understand that the senso comfort thermostat (vr720/3 i think) can do multiple zones.

 

Yes it can. Provided they have fitted a VR70 two-zone wiring centre as well(!) (big shallow rectangular white box). Or maybe they have used a third-party control setup, what schematic have they used (all are in Files section of Arotherm plus FB page)?

[Post and beam]

7 hours ago, sharpener said:

what schematic have they used

If i understand you correctly its 8. 

[sharpener]

12 hours ago, Post and beam said:

If i understand you correctly its 8. 

 

That is the  Basic System diagram number. 8 is correct without a buffer, 10 with. I was asking about the schematic of which there are a whole book of them depending on how many zones, what they are, whether an indoor unit and/or buffer. See other post with link to FB group. There is a recent post on there about multiple zones, you will need additional temp sensors as well if you want thermostatic control of room temp in them (Room Temp Mod = Active or Expanded).

Edited Friday at 09:01 by sharpener

[Post and beam]

7 hours ago, sharpener said:

See other post with link to FB group

Memory fails me dude. Would you point me in the right direction please

[Temp]

Silly question but are you getting any heat to the rads? If some then with one stat it sounds like a balancing issue. If none it sounds like a system issue like a valve off?

[Post and beam]

Waiting on a thernal camera but to be honest i have not felt any heat in the radiators. Dont expect much heat and with the current weather dont need it really. But, if there is an issue i need to sort it out soon.  At the very least i believe my supplier should have installed a second zone & control for it.

[Nickfromwales]

On 16/10/2025 at 09:31, Post and beam said:

There you go, the Booboo might have been me misunderstanding how they worked. I assumed they just did a restricting job on the water flowing through.

 

I did screw down the flow valves on the UFH manifold to the hallway and the downstairs WC last night. The WC is really quite warm. I will check later this afternoon if its made any difference yet. Going for a wired thermostat may not have been the best idea me thinks.

 

Just to say we have not moved in yet but i have been getting ready to do so this weekend.

 

Are the TRV’s set to 5, or ‘max’ for the purpose of testing?

[JamesPa]

11 hours ago, Nickfromwales said:

Are the TRV’s set to 5, or ‘max’ for the purpose of testing?

Hopefully they are!

 

Leave them that way, (better still unscrew the heads which is what I have done with all but 2 of mine); adjust the WC curve down so the house temp is right, balance the zones/loops/radiators, result:  efficient system and more comfortable house.  If you have any rooms where solar gain can be large, use TRVs as limiters  in those rooms only, by setting them a couple of notches above the target temp.

Edited Saturday at 07:34 by JamesPa

[HughF]

26degree flow temp into a new build I’ve just helped commission…. 125mm concrete floor slab, pipe at 150 spacing.

 

just an fyi.

[Post and beam]

On 16/10/2025 at 09:31, Post and beam said:

Are the TRV’s set to 5, or ‘max’ for the purpose of testing?                         Yes they are .  Can feel a little heat in the radiators today. not suprising as the flow temp will be down in the low 30's . So i think that this demonstrates there is no fundamental issue.  Still waiting to hear why the installation company did not deliver what i asked for and therefore believe i paid for. Namely, a second zone, with its own temperature control. 

[Post and beam]

Come to think of it how is the radiator hot water supplied even if there is a temperature control for it?  Surely it needs it own diverted hot water. I think i might have a bigger issue than i thought.

[JamesPa]

1 hour ago, Post and beam said:

Come to think of it how is the radiator hot water supplied even if there is a temperature control for it?  Surely it needs it own diverted hot water. I think i might have a bigger issue than i thought.

Not sure what question you are asking. 

 

Normally there is a 3 way diverter valve between DHW and space heating, fitted on the flow.  All of the space heating water circuits should connect to this.  The return is not valved.

 

No need for temperature control for the circuits, water will flow through them if they are connected!  You then balance the various circuits/radiators for same temperature (or desired temp difference) and you can operate on pure WC or WC with a little bit of room influence.   The Vaillant controls are all you really need, providing bags of well thought through flexibility for setbacks/set forwards and various ways to use the room temperature as an overlay to a system essentially run on weather compensation.  

 

 

Edited 23 hours ago by JamesPa

[Dillsue]

5 hours ago, Post and beam said:

Come to think of it how is the radiator hot water supplied even if there is a temperature control for it?  Surely it needs it own diverted hot water. I think i might have a bigger issue than i thought.

Where's your installer? Should he be explaining how he's designed/installed things and setting the system up for you??

[Nickfromwales]

5 hours ago, Post and beam said:

Come to think of it how is the radiator hot water supplied even if there is a temperature control for it?  Surely it needs it own diverted hot water. I think i might have a bigger issue than i thought.

If the rads need a higher temp to function, then you should be setting the CH flow temp for the rads, then the TMV on the UFH governs max flow temp into the floor.

 

If the system is set up to service the UFH at 30° then the rads will be doing near nothing. They feel cool / cold as your body temp is higher, so placing your hand on it is a poor point for reference; the true reference is the actual temp of the room / space, so if the rooms at the desired temp then it’s all doing what it’s supposed to. 

[marshian]

5 hours ago, Nickfromwales said:

If the rads need a higher temp to function, then you should be setting the CH flow temp for the rads, then the TMV on the UFH governs max flow temp into the floor.

 

If the system is set up to service the UFH at 30° then the rads will be doing near nothing. They feel cool / cold as your body temp is higher, so placing your hand on it is a poor point for reference; the true reference is the actual temp of the room / space, so if the rooms at the desired temp then it’s all doing what it’s supposed to. 

 

Exactly - it was a real surprise to me how effective "cold to touch" rads are as space heaters in shoulder seasons

 

I was tweaking the balance of my rad circuit this morning (since I increased my pump speed the burn times have lengthened and rooms have started to overheat)

 

OAT was 10 Deg C - target boiler temp was 27 Deg C but I increased the WC curve to extend the burn time so I could get round and measure all the rads

 

	Flow	Return	Diff	Room	Target
Boiler	32.4	25.3	7.1
Kitchen	29.8	26.0	3.8	21.0	20.5
Dining	30.8	27.2	3.6	19.5	20.0
Lounge	31.0	26.2	4.8	19.5	19.0
Hallway	29.6	24.2	5.4	19.5	19.0
Utility	25.8	22.2	3.6	18.0	18.5
Toilet	27.6	23.6	4.0	19.5	19.0
Front Hall	24.4	18.4	6.0	17.0	17.0
Bed 1	28.8	24.2	4.6	20.0	20.0
Bed 2	25.2	21.0	4.2	20.0	19.5
Bed 3	27.8	23.4	4.4	20.0	19.5
Study	28.6	22.8	5.8	19.0	18.0
Bath	29.2	21.6	7.6	20.5	21.0
Ensuite	29.0	22.0	7.0	20.5	21.0