vaillant sine 18 fault - no central heating : Help me please

Hi all,

Any advice on this problem Id really appreciate.

Friends Vaillant Sine stopped working. He had 2 plumbers round saying the boiler needed to be replaced for wrong reasons (ignitor not working no parts availalbility) etc.

Ignitor worked fine, but i found the overheat switch open circuit, so i pushed the black knob in and it started to work agaiin for DHW.

When the central heating button gets clicked though the boiler fires up for about 15 seconds, initially full rate, then half rate, then it cuts out.

I checked the signals to the pump and they run when ch is on.

Hot water seems to be being circulated around the inner boiler but not to the central heating circuit.

If I remove the nTc purple wire it fires up fine, but still doesnt circulate to the ch circuit.
It seems to me as if the water in the NTC zone gets too hot and the boiler switches off on CH, because there is no way of getting the water circulated out of the boiler and therefore it overheats. This problem doesnt occur when running dhw hotwater from the tap and it appears to cool down the heat exchanger. I dont think the NTC sensor is faulty as it only cuts the gas out when its pipe is really hot.

I tried flushing water through the rads to make sure not blocked and okay. Also i reverse flushed water from the return circuit round the rads and backwards up into the boiler and out the pressure overflow to see if flow can go that way and to dislodge any debris and it flushed backwards fine.

I am suspecting the ch valve in the divertor (behind the dhw heat exchanger) is either jammed for DHW and not letting ch water flow. Or there is some reason a sensor or something is signalling to it to remain locked in the DHW position and not CH.


Please can anyone pour light on to this one ?

Also can anyone advise where instructions or for this boiler or associated diagrams.?

Many thanks

Dave

wax capsule in 3 way valve ,but you may need full valve depending on the condition, full valve may be around 200 quid

Problem lies in the diverter valve. Sadly, the complete unit will need to be replaced, though the offending component is available, but not dure if associated seals are included.

thanks gents, someone else said it was the wax capsule component broken within the diverter valve.

My plan is to buy diverter valve (£130 reconditioned) and a wax capsule kit. Then attempt to fit them (not using the diverter if not necesarry)

Ill keep you posted soon.

Many thanks for your great advice

Cheers

Dave

The wax capsule is INSIDE the diverter valve!

If the diverter valve is genuinely reconditioned then it should be all that you need.

Tony

Thanks for the help.



Bought a reconditioned diverter valve with built in wax cartridge at the bottom. £160 but £50 returned when handing back the old knackered one. Got this from Adlink in London.



Fitted it after a lot of wrestling in a dark small cupboard (took about 3 hours believe it or not trying to angle up the compression fittings without threading them.


Anyway once in the boiler fired up and worked fine for both ch and hot water so result, and a happy cust