UFH help

[Stevenwithav]

Hi everyone, I'm new to this forum and hoping for some advice on my underfloor heating (UFH).
I recently moved into a four-year-old house with UFH downstairs and radiators upstairs. I've noticed a strange issue: the UFH only seems to heat up when the upstairs radiators are calling for heat.  For example, when the radiator timer is on, the boiler kicks in, heating the water that then circulates through both the radiators and the UFH. However, if the radiator timer is off during the day, and I turn up the UFH thermostat, I can see water circulating through the manifold, but it's only lukewarm or cold.
My system has three 2-port valves: one for the radiators, one for the towel rails, and one for hot water.  However, there 2-port valve for the UFH manifold.  It's a WUNDA system, and a cable runs from the WUNDA central connection box to the boiler, which I assumed controlled the UFH's call for heat. But clearly, it's not working as expected.
What am I missing? Any help would be greatly appreciated. I'll attach some photos of my system to give you a better idea of the setup.

(ignore the orange cable that’s an extension for something else)

 

thanks
 

[JohnMo]

Have you changed settings on the thermostat/timers since moving in?

 

I would suspect when they tried to commission the system, they would have short cycling issues (boiler only running for very short periods) when only trying to heat 5 loops of UFH, via a mixer. So they may elected to leave the radiator thermostat in charge. So all on or all off.

 

I would be tempted - assuming you have radiators TRVs to set the thermostat to run for long periods, let radiators rooms be regulated by TRVs, and under floor managed by mixer flow temp.

 

I would also set towel rads to run for the same times as the radiator thermostat is set. To give boiler the best change of staying away from short cycling.

 

Underfloor water temps are alway fairly cool to touch.

[Benpointer]

Problem with the UFH mixing valve?

[Stevenwithav]

Morning, thanks for the replies, the UFH mixing valve seems to work fine,

The problem I see with leaving the radiators thermostat in control is I   like the evenings upstairs to be cool for bed but the downstairs warm for the evening, but by having the rads go off at about 7 the downstairs gets cold, then when I turn up the UFH thermostat  it never warms due to being unable to call for heat, (I’d have thought the cable coming from the WUNDA control box to the boiler was to independently call for heat, is that wrong?)

[ProDave]

22 hours ago, Stevenwithav said:

My system has three 2-port valves: one for the radiators, one for the towel rails, and one for hot water.  However, there 2-port valve for the UFH manifold.  It's a WUNDA system, and a cable runs from the WUNDA central connection box to the boiler, which I assumed controlled the UFH's call for heat. But clearly, it's not working as expected.

In your second picture, you can see the three 2 port motorised valves all connected to what I believe is the wiring centre above the 2 switches.

 

First test.  With everything OFF, go and turn on the UFH.  Observe the 2 port valve for the UFH.  Does that open?

 

Second test, with everything OFF, manually opening the override lever on each valve should cause the boiler to fire up.  Does it?

[Nickfromwales]

2 hours ago, ProDave said:

Second test, with everything OFF, manually opening the override lever on each valve should cause the boiler to fire up.  Does it?

Just remember if you don’t do that manual push quite rapidly the mechanism won’t press the micro switch that tells the boiler to light. 
 

The lever is only there to manually open the valve for commissioning / draining down, and if you move it slowly to the latched on position the micro switch won’t get operated   

 

You’d need to push it quite quickly, and then the momentum created sends the arm past the latch position, then it temporarily presses the switch, and then drops back away from it.

 

First test as above is the starting point, then diagnosing from there will be by more process of elimination here   
 

Does sound like the motorised valve isn’t doing its thing, as the boilers not lighting but the UFH controls seem to be working as the pump comes on at the manifold, so should be easy to get the issue identified. 
 

Ask any questions and we’ll go through it step by step. 

[ProDave]

1 minute ago, Nickfromwales said:

Just remember if you don’t do that manual push quite rapidly the mechanism won’t press the micro switch that tells the boiler to light. 
 

The lever is only there to manually open the valve for commissioning / draining down, and if you move it slowly to the latched on position the micro switch won’t get operated   

 

You’d need to push it quite quickly, and then the momentum created sends the arm past the latch position, then it temporarily presses the switch, and then drops back away from it.

Ah yes I forgot that quirk of that type of valve.  So you need probably a second person looking / listening to the boiler to see if it briefly tries to start as you push the manual lever on the 2 port valve as hard and as fast as you can to make it momentarily turn the switch on.

[Stevenwithav]

so the three 2-port valves don’t run to the UFH, one is for the hot water, second for the towel rails and the third for the upstairs radiators, 

the UFH doesn’t have a 2-port valves, I think the wire coming from the WUNDA H-Box going into the bottom of the boiler is what calls for the boiler to kick in to heat the UFH, so I might have an issue with the H-Box

[ProDave]

7 hours ago, Stevenwithav said:

so the three 2-port valves don’t run to the UFH, one is for the hot water, second for the towel rails and the third for the upstairs radiators, 

the UFH doesn’t have a 2-port valves, I think the wire coming from the WUNDA H-Box going into the bottom of the boiler is what calls for the boiler to kick in to heat the UFH, so I might have an issue with the H-Box

Post some close up pictures of the wiring inside the Wunda box with it's cover off.

[Stevenwithav]

Here are the photos inside the h-box

[ProDave]

9 minutes ago, Stevenwithav said:

This terminal block.

 

The right hand pair should power the manifold circulating pump.  The manifold circulating pump should turn on when any UFH circuit calls for heat.  Does that happen?

 

The left hand pair of contacts is a relay contact that should close at the same time.  This pair or relay contacts would normally be connected in your case in parallel with the switch contacts from the radiator motorised valves and that would give the call for heat to the boiler when UFH requests heat.

 

Do you have anything like a multimeter to make any measurements?

 

Can you follow the cable that contains those black and grey cables and see where it goes and photograph whatever junction box etc it connects into?

[Stevenwithav]

I don’t have a multimeter but can see there is voltage in the right terminal which does lead to the pump, but no voltage in the left terminal which leads to the 230v junction box,

 

The grey and black wires are going to the junction box, inside the black is connected to a connector block with the orange wires from all three 2-way ports, and the gray wire isn’t connected to anything, 

[Stevenwithav]

[ProDave]

Clearly that grey going nowhere is why the call for heat from the UFH does not work.

 

You say the black from the UFH box goes to the same connector block as all  the orange wires from the 2 port valves.  That is good.  (it is not clear in your photo which one that is , i think the orange wires are looking more like brown in that photo)

 

So the grey wire from the UFH box needs to connect to the same terminal block as all the grey wires from the 2 port valves.  Make absolutely sure you are connecting to the correct set of grey wires before connecting the wire from the UFH into them.  and make sure power is off, depending on the boiler this might be switching a low voltage or might be 230V

[Stevenwithav]

The top black circle shows the connection block that the black wire is connected to, the bottom black circle shows the gray not attached to anything, 

 

if I connect the gray to the connector block with the other grays,  when the UFH calls for heat will that not open the 2-port valves allowing hot water to flow to the hot water/Rads/towel rails when I just want the UFH to heat up? 
 

thanks

[JohnMo]

1 minute ago, Stevenwithav said:

when I just want the UFH to heat up? 

Back to my original post, looks like someone has stopped the boiler being called for heat, just to satisfy UFH on purpose. Looking at your photos of the UFH manifold the only loop with flow is the lounge. So assume each room with UFH has its own thermostat also? If so your boiler will just short cycle (use bucket loads of gas with little or no heat being delivered), if you do get the wires sorted to fire the boiler with just a single UFH circuit calling for heat.

[Stevenwithav]

There are three thermostats, one for the hall, one for the lounge and one for the kitchen are (nothing is big so has three loops), in the picture it only shows the lounge has flow but all the others do usually have flow, just wasn’t on at the time of the picture, 

[ProDave]

20 minutes ago, Stevenwithav said:

The top black circle shows the connection block that the black wire is connected to, the bottom black circle shows the gray not attached to anything, 

 

if I connect the gray to the connector block with the other grays,  when the UFH calls for heat will that not open the 2-port valves allowing hot water to flow to the hot water/Rads/towel rails when I just want the UFH to heat up? 
 

thanks

Yes, but the point I was making as there are other grey wires with other functions, make absolutely certain these ARE the grey wires from the motorised valves before you connect your UFH grey wire to them.

[ProDave]

15 minutes ago, JohnMo said:

Back to my original post, looks like someone has stopped the boiler being called for heat, just to satisfy UFH on purpose. Looking at your photos of the UFH manifold the only loop with flow is the lounge. So assume each room with UFH has its own thermostat also? If so your boiler will just short cycle (use bucket loads of gas with little or no heat being delivered), if you do get the wires sorted to fire the boiler with just a single UFH circuit calling for heat.

That is looking likely why it was disconnected, but that does not help the OP, he wants the UFH to work on it's own.

 

When he gets it working then if there is a lot of short cycling then we can discuss options to make the UFH work as one big zone all on or all off.

[JohnMo]

7 minutes ago, ProDave said:

That is looking likely why it was disconnected, but that does not help the OP, he wants the UFH to work on it's own.

 

When he gets it working then if there is a lot of short cycling then we can discuss options to make the UFH work as one big zone all on or all off.

Sounds like work, to make more work.

[ProDave]

15 minutes ago, JohnMo said:

Sounds like work, to make more work.

There is no other choice if the OP wants the UFH to work without the radiators on.

[JohnMo]

2 minutes ago, ProDave said:

There is no other choice if the OP wants the UFH to work without the radiators on.

Just giving information based on doing that and paying the huge bills while understood what was happening.

 

Been there, got the tee shirt. Big zones good, small zones bad for the bank balance.

[Stevenwithav]

So do you think the installer deliberately made it so the UFH and the Rad/towel rails are all connected so that they come on together, in other words I set the Radiator thermostat to come on at say 6am which calls for heat starting the boiler, which in turn heats the Rads and the UFH? 

[ProDave]

4 minutes ago, Stevenwithav said:

So do you think the installer deliberately made it so the UFH and the Rad/towel rails are all connected so that they come on together, in other words I set the Radiator thermostat to come on at say 6am which calls for heat starting the boiler, which in turn heats the Rads and the UFH? 

We can only speculate if it was deliberate, or as is often the case, installers just don't understand UFH.  I went to "fix" a neighbours install that had been fitted by a local "renewable energy" company.  They had it set so the UFH manifold was running 24/7 even when the heat pump was scheduled to be off, i.e. the heat pump and UFH manifold were not electrically connected to work together.  It had been like that for about 2 years before he called me to work out why his heating did not work as expected and was somewhat random.

[JohnMo]

On 07/02/2025 at 13:03, JohnMo said:

Have you changed settings on the thermostat/timers since moving in?

@Stevenwithav Back to my first question?