Whistling UFH mixer valve & cycling boiler - no ABV?

[timmyk86]

Hi all,

New to this forum but hoping you could give me a hand with some issues I'm having with my UFH.

I bought a house in Nov last year that has wet UFH in a kitchen extension. It's a relatively small area with only 2 loops, total 90m piping and 2-port manifold. Manifold model is Wunda Premium with it's own gate valve and pump.

The main issue with this is that the mixer valve 'sings' very loudly when it is allowing hot water from the boiler into the manifold - so much so that it wakes me up at night.
Second issue is that it causes the boiler to cycle in bursts of a few minutes at a time, and it overshoots it's set temp (the CH water temp) by quite a bit, before dropping back to a more reasonable number. The boiler pump stays running the entire time the UFH is on.

The boiler is a Baxi Duo-Tec 24kw. There are 2 loops from this, one to the 5 radiators in the house and one to the UFH, controlled independently by separate thermostats.
If the radiator loop is on at the same time as the UFH, there is no singing and the temp on the boiler is constant with no cycling.

Of note, there is no ABV between the flow and return to the boiler (although I gather there is one built into the boiler).

I have flushed and cleaned the whole system (radiator and UFH), replaced the mixer valve on the UFH twice and fiddled endlessly with the boiler CH temp with no success.

My thoughts are that there is not enough return flow to the boiler when just the UFH is on, probably due to the lack of a ABV, and the demand on the system is very low causing the boiler to cycle.
I think the singing is due to the pressure of the water through the mixer valve (particularly as it doesn't happen when the radiators are on) - again something which I *think* an ABV would cure.

Am I on the right lines here or totally off course? Any help much appreciated. Thanks!

 

[Chalked]

We have found the only way to cure this is by doing the following.
1. Set the thermostat on the mixer to 47.
2. Turn the underfloor pump to the lowest setting.
3. Adjust the flow rates for each loop to achieve a 7 degree drop between the flow and return.
This normally cures it. But if it doesn’t fit an auto bypass valve just before the mixing valve.
Also properly range rate the boiler. This can help too

 

[timmyk86]

We have found the only way to cure this is by doing the following.
1. Set the thermostat on the mixer to 47.
2. Turn the underfloor pump to the lowest setting.
3. Adjust the flow rates for each loop to achieve a 7 degree drop between the flow and return.
This normally cures it. But if it doesn’t fit an auto bypass valve just before the mixing valve.
Also properly range rate the boiler. This can help too

Hi Chalked

Thanks for the thoughts. I have more or less done all these things - mixer is about 47 (which is what I need to get some heat through the wood floor), pump is on it's lowest setting and I've set the flow rates so they are pretty close to 7 degree drop over each loop.

I've also lowered the boiler CH temp to 50 in the hope that it stays lit and consistently provides 50 degree water...but it doesn't. The whistling and cycling continues.

Wunda have kindly sent me an Esbe valve to try to see if it stops the whistling - probably won't help the cycling boiler though.

At a bit of a loss really!

 

[Chalked]

I’ve had 6 wundafloor mixers whistling.
Even after they sent new ones it didn’t stop.
Found installing a bypass near the mixer cured it.

 

[timmyk86]

I’ve had 6 wundafloor mixers whistling.
Even after they sent new ones it didn’t stop.
Found installing a bypass near the mixer cured it.

Okay great, thanks.

Does that apply even if the boiler has a built in auto bypass valve? Happy to try either way!

 

[Chalked]

Okay great, thanks.

Does that apply even if the boiler has a built in auto bypass valve? Happy to try either way!

Yes mate. Had the same problem on an ecotec

 

[John.g]

Hi Chalked

Thanks for the thoughts. I have more or less done all these things - mixer is about 47 (which is what I need to get some heat through the wood floor), pump is on it's lowest setting and I've set the flow rates so they are pretty close to 7 degree drop over each loop.

I've also lowered the boiler CH temp to 50 in the hope that it stays lit and consistently provides 50 degree water...but it doesn't. The whistling and cycling continues.

Wunda have kindly sent me an Esbe valve to try to see if it stops the whistling - probably won't help the cycling boiler though.

At a bit of a loss really!

Just looking at this from the cycling point of view, if one assumed that your UFH is emitting 5 kw then based on your numbers above the boiler flow/return should be ~ 7 LPM & the UFH flowrate should be ~ 10 LPM with 3 LPM recirculating to give a mixing temp of 47C. If the UFH is only emitting 2.5 kw then boiler flowrate is 3.5 LPM, a UFH flowrate of 5 LPM & recirc of 1.5 LPM.
Based on the above you might consider just checking the cycling rate with the rads only in service and just keep shutting them down progressively until only one in service and see if the boiler actually modulates, when it reaches max turn down (to say 5 kw?) observe how long it runs for before cut out.
On UFH only the boiler might be reaching max temperature before it gets a chance to modulate but you probably have already looked at this. The above might tell you something.
As suggested above, range rating should help but IF its a combi boiler then is it possible to range rate the CH side & still have full output on HW??.
External ABV might stop whistling noise but I just don't know about the cycling as the boiler flow&return temps will be much closer depending on the amount of bypass.