Observations on need for heating upstairs

[Post and beam]

[Michael_S]

Back to the OP.

 

WE have rads up and down, had to use the balancing valves to heavily restrict the flow through the downstairs rads to force enough heat upstairs.  Is there a way for you to restrict the UFH flow to increase the upstairs circulation?

 

We followed advice on here to stop using the TRVs on the downstairs rads to try and achieve the same effect as it tended to just make the HP cycle more and the upstairs never got as warm as we wanted, now the upstairs is slightly cooler (20 vs 22) due to rad sizing and flow.

[Nickfromwales]

15 hours ago, Post and beam said:

That can be made to work, but I’d need more info and to understand the way it’s been plumbed / pumped / operated etc to see if hydraulic separation needs to be considered in this conversion.

 

Assuming it’s just the OEM pump in the ASHP atm, and flow and return just tee off to UFH and rads?
 

Day job for a decent plumber, one who doesn’t spend longer talking about how it ‘can’t be done’ than the job would actually take to do.
 

This is a low temp pump and mixer set, one I’ve been fitting for nearly a decade. 1” BSP connections to match your manifold.

Link

 

This isn’t a typical, much cheaper, TMV, but instead a thermo couple type actuator which responds by temp / hydraulic in a far smoother and more refined way. 
 

These don’t whine or chatter at their lowest settings like a regular TMV’s often do, so with this type of unit you’ll get very accurate, low temp control for the UFH in the slab.

 

Needs a bit of “tight space plumbing” skills, and prob to pack the manifold off the wall very slightly, but defo can be done in the room available.
 

Done these in much tighter spaces tbf!

[Originaltwist]

I know you can prove anything with facts but I'm sure that fan-coils run better on lower temperatures than rads. So before doing a radiator reshuffle may I suggest a simple 'DIY fan-coil heater' project. Just Google it. It's the green one, first on images.

[JohnMo]

You have a Vaillant heat pump, I would just install an ESBE electronic mixer (VRG valve and actuator) at the UFH manifold (you won't need an additional pump). Set the controller to do 2x zones, each with its own WC curve.  The zone for the UFH, the Vaillant controller will control the ESBE mixer as needed to follow your defined curve.  What will happen is if the radiators call for heat heat pump runs at higher temp and controls mixer to UFH.  If radiators aren't calling for heat the heat pump will reduce flow temp to satisfy UFH demand only mixer will be fully opened.

 

I wouldn't add any zone valves, leave the radiator alway open and when they don't need additional heat they run just like they are now and it keeps the water volume engaged and full circulation path for flow rate.

 

IVOR mixers are great, but you then need to run the UFH off thermostats, as it will receive a fixed flow temp and you always need operate the heat pump at radiator temps.

[Post and beam]

Thanks for the suggestions guys

[SimonD]

On 27/01/2026 at 10:01, Post and beam said:

our single zone design with a flow temperature that has not so far ever got above 38 degrees even at minus 5 in December is not best suited to radiators upstairs.

 

38C is fine with radiators as long as they're sized correctly. My system with all rads ran at 36C at -6 with the whole house nice and toasty. There are really two issues you need to consider and measure. First is the temperatures of all your upstairs radiators and compare this to your ASHP and UFH flow temps. If it's significantly lower, you then know it's a flow issue to the rad circuit and you can tackle this in several ways. If all your rads are about the same temp as your ASHP flow temp, then you know it's more likely an issue with radiator sizing. No need to spend any money right now, just do some simple investigations first.

[marshian]

2 hours ago, SimonD said:

 

38C is fine with radiators as long as they're sized correctly. My system with all rads ran at 36C at -6 with the whole house nice and toasty. There are really two issues you need to consider and measure. First is the temperatures of all your upstairs radiators and compare this to your ASHP and UFH flow temps. If it's significantly lower, you then know it's a flow issue to the rad circuit and you can tackle this in several ways. If all your rads are about the same temp as your ASHP flow temp, then you know it's more likely an issue with radiator sizing. No need to spend any money right now, just do some simple investigations first.

 

^ WHS even in the -6 we had in early Jan my flow temps didn't go above 38 Deg C and the house was comfortable

 

All rads sized for 35 Deg C flow temp at -2.5 Deg C OAT and sized to meet the heat loss of each room at that temp

[Dillsue]

7 hours ago, marshian said:

All rads sized for 35 Deg C flow temp at -2.5 Deg C OAT and sized to meet the heat loss of each room at that temp

Exactly this. Max flow temp we've seen is 34 degrees through the cold days we've had and the living areas been at a steady 21 degrees since early november

[Nickfromwales]

11 hours ago, JohnMo said:

IVOR mixers are great, but you then need to run the UFH off thermostats, as it will receive a fixed flow temp and you always need operate the heat pump at radiator temps.

No you don't.

 

The (then higher) fixed flow temp will arrive at the TMV, and the UFH will see zero change in circumstance or performance. The FF rads will receive x degrees higher flow temp and actually do something.

 

The rads go on TRV's to manage the difference in the size of the spaces that they are now able to satisfy.

 

You balance and attenuate the lift in flow temp degrees at a time, until the happy medium is achieved.

[JohnMo]

10 minutes ago, Nickfromwales said:

No you don't.

 

The (then higher) fixed flow temp will arrive at the TMV, and the UFH will see zero change in circumstance or performance. The FF rads will receive x degrees higher flow temp and actually do something.

 

The rads go on TRV's to manage the difference in the size of the spaces that they are now able to satisfy.

 

You balance and attenuate the lift in flow temp degrees at a time, until the happy medium is achieved.

So you are saying to run everything at a fixed temperature, with TRV's on rads and how are you managing UFH room temps, thermostats?

[Nickfromwales]

13 minutes ago, JohnMo said:

how are you managing UFH room temps, thermostats?

I'm not, the OP didn't say there was an issue there  

 

13 minutes ago, JohnMo said:

So you are saying to run everything at a fixed temperature

That's what they have now!!!! 🙄😉

[JohnMo]

On 27/01/2026 at 10:30, Post and beam said:

WC @ .45, on all the time.

 

11 minutes ago, Nickfromwales said:

24 minutes ago, JohnMo said:

So you are saying to run everything at a fixed temperature

That's what they have now!!!! 🙄😉

No, it's run on WC, not fixed flow temp, so fixed flow temperature would be completely different, may need a buffer if you are messing flow with TRV etc.

[Nickfromwales]

WC will still prevail. Currently the rads are strangled.

 

13 hours ago, Nickfromwales said:

but I’d need more info and to understand the way it’s been plumbed / pumped / operated etc to see if hydraulic separation needs to be considered in this conversion.

One step ahead, my man.........