Suprima Overheating and Locking Out - Not PCB

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18 Nov 2007
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Liverpool
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Hi all,

Great forum, I have done many searches on my suprima problem. So far, I have replaced the PCB but it hasnt cured the problem. Basically my system works well for about 40 mins from cold but then locks-out. After pressing reset it re-ignites for about 5-10 mins and then does the same thing (locks-out). After some research I think I need to replace the thermistor and/or the Overheat Stat. After looking at the thermistor it has lots of white gunk on it (see pic below - IS THIS NORMAL?)

Also, am I on the right tracks? Cheers. Sam

yqt8wn.jpg

yqt8wp.jpg
 
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The white paste is to improve thermal conductivity and is normal.

You can try changing both the thermistor/overheat stat. These are often changed by boiler engineers when changing the PCB or, if your problem relates to overheating it could be the pump.
 
If you have pulled out the thermistor then its essential to replace the thermal paste.

They rarely fail and it could be just that it needs packing with paste.

I once advised a sceptical engineer to add paste and he later called back to confirm that it had solved the problem.

Have you measured the temperature differential on the flow and return? It may be a failing pump or blocked system reducing the flow rate. The differential should be no more then 12-13°C.

I do have to say that your PCB certainly does not look at all new!

Tony
 
Yes, Tony, that is either the 'old' one or it is an ebay special.

Can the OP confirm when he changed the PCB and tell us about its provenance?

The new ones are a Siemens unit in a plastic box.......
 
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Thanks for all the replies. I am pleased to say that the problem is now fixed!! It looked like it was down to one of the micro-switches in the motorised valve that was causing the lock-out. I noted that the CH would not come on , on its own so swapped out the valve - et voila!! Changing the PCB was prob not necessary but for £30 it was worth covering that base. I got the recond PCB from eBay. Its not the new one but seems to be working very well.

Cheers all.
 
well it dont look like a good recon to be with that browning going on, but each to his own I suppose
 
I had the lockout problem return again after previous replacement with a new PCB and a new pump. Got overheating lockout with flashing red light. Simple remedy is to turn down boiler thermostat to no more than 4 o'clock position & turn down thermostat on hot water tank to 50C. Examined thermistor which was working OK but made sure plenty of thermal conducting paste was rammed into sensor hole as system overheats if thermistor is not in good contact with water pipe on boiler. Lockout can also be caused by poor gap setting on electrode which should be 3-4mm - this can be cautiously bent with pliers to get correct gap. While in there good idea to vacuum any dust on gas jets. this mini service solved problem & no lockout since.
Overheat thermostat also tested with multimeter and had open connection - may be error in potterton manual as it says if <60C then there is continuity between the connections! I tested a new unused overheat thermostat & this did not have continuity at room temperature.
PCB fitted in 2007 was part 5111603.
 

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