Non firing boiler.

[Cotranz1]

Hi all. I have a 2 zone UF with its own pump and wiring centre. My main CH and HW work from the main wiring centre which has its pump. All 3 switched live orange wires come through this WC to a set of linked terminals which lead to teminal 13 from which are the connection to the pump and boiler. CH and HW have one control box and the UF has its own. The problem: CH and HW are working perfectly but although timer, valve and pump in UF are all functioning only the pumps are coming on but the boiler is not firing. I can not explain how current at 13 turns on the pump but not the boiler with both wires firm in terminal and it being exactly the same route for HW nd CH. We do not think there is a blockage as the heat does come down to Uf if it is first triggered by òne of the others. Today I listened intently and thought I heard a recurring but speedy lessening of pump sound almost a hiccup . Could I have heard right and could this point to the problem? Any suggestions would be most welcome as I and my electrician are mystified.

 

[ProDave]

Have you actually measured voltage at terminal 13 when UFH only is demanding? If the pump is running slow and the boiler not firing, my guess is you don;t have full 230V there, which could be a faulty feedback switch in the UFH motorised valve, a very common fault.

 

[Cotranz1]

Have you actually measured voltage at terminal 13 when UFH only is demanding? If the pump is running slow and the boiler not firing, my guess is you don;t have full 230V there, which could be a faulty feedback switch in the UFH motorised valve, a very common fault.

Thank you for taking the time to read and think about this. I will check this.

 

[kerching]

As @ProDave has mused. UFH zone valve end switch is most likely goosed. A trick,that often works is to HARSHLY and FIRMLY force the override switch on the valve and see if the boiler fires for a split second

 

[Cotranz1]

Thanks...am folowing up on this