Worcester 350 combi help

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hi, I have a 1991 worcester 350 combi that has developed an interesting fault, that I could do with some assistance to pinpoint to source.

After drawing hot water through the taps the boiler fails to return to central heating. The demand light remains on and the pump is running, but there's no ignition.

If the programmer is modified through "off/once/twice/on" then the central heating comes on straight away without any issues, but as soon as any hot water is taken it fails to re-ignite.

Thanks
 
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sounds like its forgetting to start up after its anti-cycle delay. would've thought it would have done it on CH too though.
 
Tried disconnecting the flow switch but it made no difference.

Yes I thought it must be a logic fault rather than a sensor or relay, but on which board is the logic located.

Not sure if I made it clear about what is happening. Starting with CH on, after HW is drawn off the CH never comes back on. But if the programmer or room stat is cycled, so that the demand light is extinguished and then re-lit the CH fires up again.
 
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yes but what i meant was if the sequence board had failed i would have thought with CH on and NO HW demand the boiler would fail to ignite once the CH had reached temp then tried to re-ignite after its anti cycle delay.

i have to admit i can't remember if that was the case last time i changed a sequence board for this fault as it was years ago. perhaps it has a different sequence for HW demand.

sequence board is my guess, change it at your peril :LOL:
 
Just read through, sounds like it's stuck in anti cycle mode to me too. It's the driver board that causes this fault though, not the sequence board.

The driver board is about £125 and the sequence board it £110 ish, if you don't want to take the risk BG will replace which ever board they think is causing the fault for about £180. Plus, if they get it wrong, they'll change the other for nothing!
 
Just read through, sounds like it's stuck in anti cycle mode to me too. It's the driver board that causes this fault though, not the sequence board.

The driver board is about £125 and the sequence board it £110 ish, if you don't want to take the risk BG will replace which ever board they think is causing the fault for about £180. Plus, if they get it wrong, they'll change the other for nothing!

bah, apologies if it is the wrong board. :oops:

p.s. if i turned up you would get both boards changed first time. lost count of how many times ive changed one and the other one goes the week after.
 
Thanks guys, think I'll look into the driver board.

Thankfully the weather has warmed up lately so the pressure is off to find a quick solution, and I can simply turn the room stat down and back up again to get the heating back on if we're desperate

I'll post an update when I've done the work.
 
Just thought I'd update everyone.

Andygasman was spot on. I got BG in though (right again); by the time I'd bought the board and paid P&P the price difference wasn't enough to encourage me to do a DIY job instead of having a guaranteed repair by the professionals. They swapped the driver board - fault fixed.

Thanks
 
BG did something right!! :D :D :D

Bet there wont be 10 pages of people chipping in their 2 pence worth about BG on this thread ;)
 
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