Alpha 240E - no hot water -> replace main PCB?

[juliald]

Hi All,

I'd be v grateful for your advice.

My Alpha 240E has stopped giving hot water. Its been flakey for a while but seemed to work if the heating was on for 5 mins beforehand. Now it hardly ever fires up and when it does it turns off again after a few secs.

Looking at other forum posts you generally recommend repair to the diverter valve, flow valve diaphragms or microswitches. However these all seem to work (pins pop out at the right times and there is continuity across the switches when pressed).

When I turn the tap the hot water neon comes on, both flow valve pins are out and pushing the microswitches and the pump runs. However the fan only occasionally spins, and following the service manual - the microswitches and temp sensors measure fine but there is not 240V across main PCB M3 16 & 19. The fan works fine with the heating on and then there is 240V across those terminals.

This points to replacing the main PCB.

However... my boiler knowledge is based only upon watching it being serviced, the service manual, forums, and poking about with a multimeter. Therefore I'd value some more experienced second opinions.

Also this problem has happened intermittently before, and the fan does run occationally now, would a PCB fault come and go like this?

Another problem is that the heating sometimes fires up randomly, with the heating neon not lit. It can click on and off several times. This can happen when the selector is on hot water only. This is a pain but not so bad as I can just turn the system off, but could it also indicate a faulty main PCB?

btw - I will be getting a pro in to do any work, it's just my gas man didn't manage to diagnose or solve the random firing up problem last time he came so I'd rather have some idea of what's going on ahead of calling him.

Thanks

Julia

 

[gas4you]

Alpha pcb's are very reliable, although I've had to swap out 3 on the CB series recently.

I personally wouldn't be looking at the pcb yet, especially as it checks out when ch is on and you need a mortgage to buy one. Typical Alpha over priced spares

I would want to re-check the microswitches, both, and check for any bad wiring connections first.

You could also change the primary thermistor.

I've had many of these that read the correct resistance, but break down when in use. It is only about £10-£15 for the ntc.

 

[juliald]

Hi Dave,

Thanks so much. I rechecked the microswitches & thermistors. The DHW thermistor was reading much too high, and on closer inspection it was leaking slightly which had caused corrosion. If I put an 11kohm resistor across then the hot water fires up fine. And the new thermistor will only be about £10.

Fingers crossed that will work. Then you'll have saved me over £100! Thanks again

Julia