Problems with new style Potterton Suprima PCB

[goosander]

After experiencing the usual lockout problems, I replaced the PCB on my Suprima 40 with one of the style ones (part no. 5111506). The boiler has been fine for the last three years but is now playing up again.

Sometimes I get the flashing green light (temp satisfied) almost immediately after the boiler fires up when the water is still cold, other times the boiler indicates no external call for heat when there definately is.

I suspect that the PCB is faulty but am open to other suggestions.

If it does turn out to be the PCB, have I just been unlucky in having a fault develop, or are the new style PCB's as bad as the older ones?

 

[simond]

You need to check that you are getting a 'call for heat' from your building controls on the SL connector.

Only then can you blame your 3yr old PCB.

You could have an intermittent pump, for instance.

But it is not unknown for any Poxi Batterton PCB to throw in the towel, 3yrs is a lifetime in their eyes!

 

[goosander]

Looks like it isn't the PCB - just checked SL and there is only 150V there when the CH only is on as compared to 240V when HW is on which suggests that either the switches in the CH zone valve or the wiring is at fault.

It seems that the drop in voltage to 150V at SL confuses the PCB resulting in the temp satisfied condition. Boiler seems to work fine when HW is on and there is 240V at SL.