worcester bosch 28 si mk2

19 Aug 2005
Reaction score
United Kingdom
I fitted this about 5 yrs ago and it now has an intermitent fault and it goes to lockout , the fan runs then it doesnt try to ignite and it goes to lockout , I have checked the fan is ok the tubes are ok and the air pressure switch semms ok , I have now proved that the air pressure switch is ok by looping out the wires to the switch and the same thing happens , I then thumped the boiler on the circuit board housing and it is now running , last time I did this it ran for four days then the same thing happened , so i now think it has a faulty pcb , anyone else think of anything else it could be ??????Cheers
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Sounds like a sticking relay on the pcb, unless you thumped it so hard that it was the gas valve sticking. When it wasn't firing could you see/hear the ignition 'ticking' :?:
No the ignition wasnt ticking so I think it is a sticking relay on the board
If ignition not working are you completely sure aps is working. some of these are not able to be 'by-passed' to test :!:
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yeah i think so as it only has two wires conected to it and the switch has to make a circuit when the aps is activated so looping it out should bypass it
ok, some of them have 3 wires to them. I am not particularly a Worcester expert. Next time it goes off try removing the pcb cover and gently tap each relay with an insulated screwdriver ;)
Hi, had the same problem with my 28si which I posted about yesterday, (newbie) This post actually helped me diagnose that the problem was a relay, one of the white one's next to a terecotta componet block?

By simply pressing on this component with an insulated screwdriver, the fan would kick in and the boiler which was constantly ticking would fire up. I was able to fill a cast Iron bath by wedging the relay with the insulated scewdriver much to my 8 year olds disgust.

Could this be repaird? Or would it be better to contact Worcester Bosch for their £185 menu repair and bite the bullet.

Please advise.
I replaced the pcb on this boiler in march and it has worked fine since , so it was definatly the pcb and not the aps
This could be repaired but I think £185 from worcester is the simplest and possibly the cheapest solution.

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