Another Suprima 50 problem

[GeorgeS]

i have a suprima 50 for 8 years and like the most of us i used to have the lockouts problem. i managed to get rid of them by re-soldering the PCB. everything worked fine up until a few weeks ago when the boiler simply wouldn't 'heat' (not sure what the exact term is ) as if the water was hot enough although it was cold.
is the cause of my problem more likely to be the PCB again or the temp sensor?...or something else..

Many thank for your help

George

 

[GeorgeS]

any idea anyone?

 

[ChrisR]

Well if it isn't the board the fault finding guide should lead you to it. Just about anything could have failed.
See partsarena.com/baxi

 

[weareleeds]

If blr not producing heat suspect pcb or thermister are you sure it isn't shutting down because of pump failure

 

[GeorgeS]

thank for your replies
the pump was replaced a few months ago and the water seems to be circulating fine.
my problem is that there is no call for heat when the water is cold. i'm gona replace the pcb first and then the thermister.
what is the latest pcb p/n that is known to be reliable? where is the best place on the net to buy it?

George

 

[ChrisR]

i'm gona replace the pcb first and then the thermister.

You'll feel a prat if it's the thermistor then!!

You can measure its resistance, which should be 500k - 1M ohm cold iirc. If you disconnect it the boiler would think it's cold and come on.
We would also check the overheat stat, flow switch, fan, aps, gas valve and thermostat pot& switch. All much cheaper than a new pcb.

 

[GeorgeS]

thanks chris. the problem is intermittent that's why i suspected the pcb.i'll check the thermistor tho. i have been looking for the installer doc for the suprima but i only found the user manual (or the installer one but for suprima HE which seems quite different).
Any idea where i can get it?

 

[simond]

Couple of years ago, we bought a Gunsons fuel injection decade resistance box. About £40.

Just connect it in place of a suspect thermistor, dial the resistance the boiler expects, and see if it sorts it.......

Saves running back to HRPC. Of course, sometimes the HW and CH thermistors are the same and you can just swap them, but it is a simple and useful tool. Just add spade crimps and away you go.


I the case of Suprimas, it is such a common problem (PCB) that we always have a 120 and sub 120 PCB on the shelf and try to make sure the chap has it on the van. 80% chance of failure, I reckon.

 

[Agile]

Its cheaper to make up a resistance box with pots and then you can just turn the pot to the required value.

Bits available at Mapline althouth I use precision wirewound components.

Tony

 

[ChrisR]

sometimes the HW and CH thermistors are the same

Suprima only has the one of course.
Agree it's overwhelmingly likely to be the pcb, especially if it won't reset sometimes.

 

[GeorgeS]

i followed chris's advice and un-plugged the thermistor. guess what? it works. the gas fires up . i also measured the resistance of the thermistor and it reads 850kohm which is within the range that chris gave me.
now, since the thermistor seems ok, can i assume that the pcb is the culprit?

george

 

[geoff@cetltd]

time to google for a reconditioned suprima pcb ...