Potterton Suprima 80, problems after flushing

[garyl]

Hello,

I’ve got a couple of problems with my CH system and would be grateful for your advice. I’ve got a 5-6 year old Potterton Suprima 80 system boiler feeding 16 radiators and a 210l Megaflo. There have been no previous lock-out problems.

Towards the end of last winter the boiler over-pressurised and vented on a couple of occasions. I assumed this was due to overheating caused by sludge building up as one of the radiators was taking longer to warm up than the others and the bottom of the radiator remained cool, so I increased the pump speed and that has kept me going ok up till now. Four weeks ago I added a litre of X400 and today attempted to flush the system.

I ran the boiler briefly this morning, turned it off at the mains, drained it down and flushed it through. I then topped it up, ran the briefly boiler again and repeated the process and finished off by adding 1l of X100. I then re-pressurised the system, switched it back on at the mains and tried to run the boiler. I set the programmer to run and turned the room thermostat up to call for heat but the boiler refused to light. It ran through the lighting sequence three times then locked out. I’ve tried using the reset button and turning the power off and on several times but each time it locks out after three unsuccessful attempts to light.

Can you please suggest what could be causing the lockouts?
Also, there is an automatic air vent on the primary return out of the Megaflo. After re-pressurising the vent is now continuously dripping water. The system was only re-pressurised to its original pressure of 2bar. Any suggestion why it should leak now? It has never dripped before.

 

[Agile]

Sounds as if you did not bother to vent the pump!

It may need spinning now.

See FAQ section.

Tony

 

[garyl]

Tony,

Thanks for the reply.

I did bother to vent the pump. Any other ideas?

 

[ChrisR]

Your boiler not lighting wouldn't be caused by current air in the pipe. So your boiler has gone wrong. If it lights then overheats, that's different.

 

[garyl]

After I flushed the system for the second time today the boiler will not light at all. It doesn't light then overheat. It hasn't overheated for several months but that was what prompted me to flush it. It worked ok this morning and after the first flush. The pump runs when I turn the system on at the mains and runs continuously even after resetting and locking out. I bled the system carefully after refilling but is it possible that air in the system would prevent the boiler from lighting at all?

 

[Agile]

Chris has told us that the Suprima runs the pump continuously after it thinks its has overheated. Thats assuming the pump is correctly wired to be operated from the boiler to give an over run.

I dont know if there was a statement on what it does with the pump after a failure to ignite.

Do you see any ignition sparking through the viewing window?

I hope you did not tamper inside the boiler at all?

Tony

 

[ChrisR]

but is it possible that air in the system would prevent the boiler from lighting at all?

As 3 posts ago, NO.

If the pcb is working (big IF) then pump would not continue running after failed ignition attempts - that's what Potty say anyway, (so it could be wrong!)

I would have thought that for an 80,000 boiler the pump would have needed to be at full speed, so that may have contributed to "overheats" if there was sludge restricting circulation as well.

It's possible that making the overheat cut out operate a few times would make it fail - sometimes they do that. Worth checking, not difficult.

 

[garyl]

Tony/ChrisR,

Thanks again for your replies.
No, I've not touched the boiler at all, other than press the reset button.

There is no visible spark when the boiler attempts to light.

The wiring of the pump is unchanged - same for the last 5-6 years.

I didn't say "the Suprima runs the pump continuously after it thinks its has overheated" I said "The pump runs when I turn the system on at the mains and runs continuously even after resetting and locking out." It doesn't overheat as it doesn't light. It hasn't overheated for several months.

ChisR.
Can you please elaborate on how to check the overheat cutout? Can I simply bypass it temporarily by connecting the two white leads together or do I need to disconnect the two white leads?

 

[Agile]

""""The pump runs when I turn the system on at the mains and runs continuously even after resetting and locking out." It doesn't overheat as it doesn't light. It hasn't overheated for several months. """

If what Potty told Chris is correct ( big IF there! ) then either your pump is wired wrongly or the PCB is not acting correctly.

Can you see if the pump is correctly connected to the boiler choc block ( tag 2 if I remember correctly ? )

I would not recommend bypassing any safety device!

The correct method is to test it for continuity with a meter! ( Or I suppose a torch bulb and battery ! )

Tony

 

[garyl]

Tony,

The pump only started running continuously when the lock-out problem started yesterday. It's worked correctly for the last 5-6 years including the timed over-run when the boiler shuts down.

Regarding the overheat thermostat. I didn't intend running the boiler with it disconnected only to test it which I've now done (with the leads disconnected) and there is a circuit. I also tested the boiler temp sensor for continuity (again with the leads disconnected) and on this sensor the cicuit is broken. Can you advise whether there should be a circuit or not on both.

 

[Agile]

The temperature sensor is a resistor which varies its resistance inversely with temperature.

At room temp ( 20 C ) I think it should be 100 k whereas most boiler sensors are 10 K or 1 K.

It sounds as if your PCB has failed again!

But there is something that we have all forgotten to mention to you. If the fan is running then it has to operate the air pressure switch before the boiler sequences further. They rarely give trouble on your model so we all forgot it.

If you blow jently TOWARDS and not into the air tube then it might bring it on. I am thinking its a positive pressure test. Blowing into it will break it!

Tony

 

[garyl]

Tony,

Thanks for the info. Sorry for the delay getting back but I had to order some bits.
Anyway -
1. Tried blowing gently towards air tube - no change.
2. Re-bled system - just in case.
3. Re-checked ignition spark - sparking ok
4. Replaced overheat thermostat - no change
5. Replaced thermistor - no change
6. Replaced PCB - no change

Boiler continues to go through lighting sequence then locks out when burner does not light after three attempts. There is no smell of gas at the outside vent following attemps to light so it doesn't appear to be an ignition problem.

Any suggestions?

 

[Gasguru]

The gas is turned off - check meter control valve or did you isolate it at the boiler.

Or the gas valve is faultly (these are the second most unreliable part after the pcb's.

 

[garyl]

Hello Gasguru,

Gas supply to house is ok - cooker is working. I didn't touch the isolation valve and it's still in the ON position. So it looks like I'll have to get a Corgi in to replace the gas valve. Thanks for your help.