Worcester Bosch 28CDi CH mostly good but intermittent fault

[daveonlyme]

7 years old Worcester Bosch 28CDi (with 2 speed fan I believe)
I’ve had intermittent CH problem since switching on CH after summer, before was ok. DHW is great- no problems. When CH is switched on (timer or manual) it works for a couple of minutes ,I can feel temperature in radiators start to rise a bit , then boiler stops with rapid flashing warning(5flash per second) on DHW demand (red LED). I reset it by power off/on switch, same thing happens stays on for a couple of minutes then fails, but when I reset again fault goes away and CH stays on all evening giving good heat ,running quietly. Fault only occurs when CH first switched on for the day.
I’ve checked flue for blockage and APS air pipes which have no cracks and no condensation. Manual says it’s fail point J –Air pressure fault. Was thinking of replacing APS and then if no good calling out WBosch in case it’s PCB failure but has anybody seen this fault before or any ideas what it could be. Can sludge cause this?
Cold pressure 1.2 bar hot 1.5

 

[Gasguru]

Take the fault codes with a pinch of salt - there're often wrong.

Could be some strange sensor fault but it may be worth calling out Worcester since boards on these are megabucks.

 

[daveonlyme]

Thanks for advice GG will definitely get their fixed fee rather than pay for board plus labour. Heard the APS ticking/clicking just before fault occurs so may try getting APS changed first as that is not megabucks i hope.

 

[undercover]

Could be a faulty C/H sensor??

 

[Agile]

For the price of a sensor I would say its worth getting a new one and connecting it off the pipe for a few seconds to see what difference it makes.

I do not expect it is the PCB and a competent boiler engineer would test everything else first.

Tony

 

[simond]

I bought one of my chaps a Gunsons resistance simulator (intended for car fuel injection systems) and it has proved useful inserting it into boilers as a temp replacement for suspect sensors.

It has saved a few unnecessary journeys. As some clown suggested last time I mentioned this, you could also cart a resistance decade box around but these tend to be bulky and expensive.

 

[daveonlyme]

Thanks v much one and all for advice. What did we do before internet ?

 

[oakland99]

i must admit i have had quite a few of these boilers with this fault and it has been the pressure switch, however i did have one when the fan was sticking first thing in the morning, it gives the same fault light flashing fast

 

[daveonlyme]

Thanks Oakland99, it clicks a lot before it fails but when boiler reset and working there's no clicking noise so i'll get a new one and take it from there. Appreciate your input.