Boiler overheating

[farfromhome]

Renovating a house and just moved in, thinking I'd finished with the plumbing, but there seems to be one remaining glitch.

I've had the existing combi boiler (Wickes combi 2000 - actually a rebranded Halstead Quattro) moved and I've replaced most of the plumbing. Hot water is fine (my wife loves the new shower!), and the radiators are doing fine so far, but when I finally finished the warm water underfloor heating and ran it (alone - the CH was off) for a couple of hours the boiler overheat trip thingy activated. I left it a few minutes and reset but it happened again. Haven't tried the UHF since, but everything else is still working fine.

Have 2 zones (CH and UHF) - separate controller and 2-port valve for each. The UHF is a small area kit made by Myson (mini-manifold with pump and blend-valve) and seemed to be ok (was getting warmer) until the boiler complained.

My guess was that I needed a bypass - the UHF would be demanding more heat than it can use so something has to take the heat away from the boiler. However the boiler manual says it has a built-in bypass.

Any ideas please? Apologies for the fairly lengthy explanation - I hope it's clear enough!

 

[corgiman]

are you sure all the valves on th UFH are open?

 

[farfromhome]

I'll check this evening - I think so though (afterall, it did appear to be working for a good couple of hours). I'm going to try turning the stat on the boiler down a bit too if I can't spot an obvious problem.

 

[farfromhome]

I hit other problems and couldn't give this the time for a while, but it seems ok now. I turned the control for the CH temperature on the boiler down most of the way (but left the HW up) and increased the temperature on the UFH blend valve - thinking the UFH will use more of the heat the boiler delivers (but for less time I guess). Since then I've had no repeat of the problem at all - and I've had it running for a few weeks.

Thanks for your response corgiman! I have to say this forum has been very helpful - I feel I've learnt a lot from reading through other posts, and the wife seems happy with the warm house so that's a result!