Hi,

 

I will email the heating engineer in the morning, but if anyone knows a simple fix I can try it today.

 

We have 4 UFH manifolds, all has been fine until Friday.

 

The kitchen seemed cold. I thought the thermostat maybe wasn't calling for heat correctly and checked that out.

 

It still seemed to be slow warming up, so I went to the manifold and turned the flow up slightly.

 

What seems to be happening is that if you turn the flow up past a certain point the water stops flowing.

 

Basically any higher than 2 on the mixer which is 22-23C and the flow stops. Even then I had to jack the pump up to maximum to get much flow.

 

The other manifolds are set between 36 and 42 and running as expected.

 

Probably wasn't an issue until the temperature dropped below zero.

 

Any thought?

Automatic bypass on the manifold playing up ?

Thanks Nick. What is that?

Or maybe the impeller on the pump

has become partially detached. 

 

An Automatic bypass is sometimes fitted into the pump / blending set ( the pump group connected to the two manifold rails ) to allow the pump to continue to run when only a few or a single loop are calling for heat. 

Depends on the make / type of set was purchased. 

Any link to the MI’s ?

http://www.wundafloorheating.co.uk/wp-content/uploads/2017/02/Wilo-Pump-Yonos-PARA-Operating-Instructions.pdf

 

The pump is running fine, then as you increase the mixer temperature you can hear hissing in the pipes and the flow stops. The pump remains on but I think it stops actually turning

It does sound like the impeller isn’t turning / seizing somehow. How long has it been running for?

Just coming up for a year.

 

But why would it only stop when I turn the mixer valve up?

 

I am going to turn it again to listen to it, thinking about it, it sounds a bit like a ball valve closing as I turn the mixer valve.

 

Certainly though it was working fine so maybe something is now wrong with the pump.

Or the blending valve. 

Pump would be my first thought so just isolate it, swap it for another and see if the fault stays or follows.  

Swap it for another already existing, there, known working one I mean  

OK. I went and listened to it and turned it the mixing valve up and down.

 

Up to around 1.8 on the mixer valve I get the normal flow rate of around 3l/min.

 

As the valve passes through 2 it hisses slightly like a closing valve and the flow rate begins to slow down. Past around 2.5 the flow collapses to 0.5l/min the stops.

 

I am guessing this means that the mixer valve is broken?

 

The pump runs all the time and as we have maximum flow below 2 on the mixer valve it seems OK.

Edited February 3, 20197 yr by AliG

Sounds like air in the system to me.  Is this manifold higher than the others?  So flow is okay when not calling for heat, it just circulates the (cold) water around the loops but as soon as the mixer opens up demand from the hot feed, it just gets air.

 

Check the system pressure (assuming a sealed system) and try opening the manifold air bleed valves.

It is on the ground floor, there are two manifolds on the ground and two on the first floor.

 

It is a Te-Sa manifold. Having looked at it I cannot see an air bleed valve. The valves I thought were for air bleed were just for filling.

Edited February 3, 20197 yr by AliG

I doubt it’s air - sounds like the mechanism inside the blending valve. 

 

Got a photo..??

That's the blending valve in the first photo there. Happy to post a different pic if it helps.

 

Having looked on line I wonder if there is simply dirt in the mixer valve.

Having looked at the manual for the pump, if you put it on the central setting it runs for 10 minutes automatically bleeding the pump but not the system.

 

I have run this anyway just in case it helps.

Edited February 3, 20197 yr by AliG