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CANT GET UFH to work!!!

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mylocalplumber

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hi,

Ok so have a 4 bedroom house.

Vaillant System boiler 637

No rads just underfloor heating. 3 x manifolds and nothing too big.

UV hot water tank.

Client complained that UFH has never worked properly.

I found system to be surprisingly dirty. Pumps knackered.

I replaced all manifold pumps, pump on boiler, removed actuators, replaced balancing valves and flow meters. Through all of these steps it always produces a new problem.

The issue I have is that the boiler keeps cutting out. Apparently it’s noticibg to small a differential temperature on flow and return. I’ve added a bypass to system which hasn’t helped. It will ramp up to 70 when asking for 60 and cut out. There’s no restriction on the system and Vaillant can’t give me an answer. Seems as though heat exchanger ok, but thing won’t stay lit. I’m at wits end. I understand that UFH has never known to work by client so I’m in the clear there but really do t want them to spend all this money and I can’t get it up and running. If anyone can help me brainstorm this one I’d be much appreciated.
 
Boiler is to big how is it piped a low loss header ? you could try down rating the boiler its in the installation manual how to do this or ring Valliant technical they will talk you through it i would try 24kw this is enough . Do you have zone valves and a auto bypass valve at the UFH manifolds the heating load needs somewhere to go even if it modulates right down the boiler needs the facility for pump over run , sounds like a design fault put some pictures up bud .Cheers kop
 
:(Note to one self, read OP’s post properly
 
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What make is the manifold, in fact pictures would be better.?

Lots of pics, pipework at boiler any valves, manifold etc.
 
Hi,

Have tried down rating at quite a few different kws. Currently at 12kw but no help.

It’s a polypipe manifold and have spoken to them but no help.

Hot zone valves at each manifold. 1 bypass internal to boiler and additional bypass near to boiler.

Will try and attach some pics on laptop when I get home as can’t work it out on phone.

I was thinking low loss header the only way forward but really want to give customer a difinitive answer.
 
Does it look like this manifold?

828939D0-89D3-4F79-8239-108076AF417E.png
 
If it does, have you removed the filter from the top and checked for debris?
 
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