Worcester 28si II shutting down on ch demand

[telelec]

Hi , problems with my boiler , all seems ok when we just demand DHW , i have had the tap running for 20 mins and all ok. When we put CH on , this can work from anything between 10mins to 1 hour , when the boiler locks out the indicator light is flashing once per second. After turning off boiler for approx 3 mins then restarting and resetting the boiler does restart ok , but when CH is demaned againg after a while it will lockout again.
Me trying to be logical and that the DHW seems ok has dismissed the gass pressure / gas valve / low water pressure / flame sensor / ignitor / APS as it all works OK for a while and works fine when only DHW is demaded. I am left with 2 options... a faulty pump ( i can hear the pump running ok NOT NOISY but it does feel hot to touch) or the Primary CH sensor located on the heat exchanger.
Is there any way to test these 2 items or am i going down the wrong road altogether and my logic is incorrect ???
Many thanks in advance for any help.

 

[telelec]

I have carried out all tests in the service manual on test d , I cannot test the gas pressure , but assume this to be OK as hot water runs fine , resistance between pins 1&2 & 8&9 was around 75 ohms and i have continuity between 6&7.
I sat and watched the boiler when i 1st turned on the CH , after about 10 mins i could hear the APS click , then electodes spark.... the flame was dying down when this happened... it did this a few times until the flame went out and the boiler locked down with the indicator light flashing once a second.

PLEASE PLAESE help ... according to the service manual this could now be a PCB fault , it says replace that , if that dont work replace gas valve... dont fancy forking out for both of them.

 

[telelec]

DHW has gone aswell now... ran for 10 mins and boiler has locked down and i cannot get it to restart now..... any advice PLEASE

 

[telelec]

anyone have any idea???

 

[Andygasman2010]

Intermittant ignition lockout is an awkward one for anyone. You could do every possible check and all could pass but because it's intermittant you won't necessarily find it. All anyone can do is go by experience and have an educated guess!

Other than what you've done, the gas pressures need checking and the electrodes need inspecting. There is a pair that you can see through the sight glass but there's a sensing electrode at the back you can't see without removing the combusion case.

It may be that the burner isn't cross-lighting propperly therefore not rectifying (this basically means the pcb can't see the burner is alight)

Not worth forking out for parts without checking this really, a job for an RGI i'm affraid!

 

[telelec]

well i gave up and have phoned worcester , they are doing a call & fix plus 12 months additional breakdown cover and parts on boiler for £279 payable monthly which i feel is quite good and gives that bit of protection and at least they should have the parts on the van unlike BG who always have to order the parts in when they come out to my mums worcester.

 

[Andygasman2010]

Yea Worcester are pretty good with their support. BG cover almost every boiler out there so it's impossible to carry everything on their vans, Worcester don't need as much.

 

[telelec]

Just an update incase anybody picks this up on a search... the problem was the PCB board , anyway the Engineer replaced that and also the fan and the APS , as he said slight faults with these can cause the PCB to go , so all 3 pats replaced plus another 12months breakdown cover on boiler for £279... an excellent service from Worcester i think.

 

[telelec]

It was the PCB , the engineer also replaced the Fan and the APS , as he said these can cause the pcb to go, so all 3 parts plus another 12 months breakdown cover (Parts and Labour) all for £279 , an excellent service from Worcester and would recommend them to anybody with a Worcester boiler.