Potterton Performa 24 - Cutting Out / HW Feeding Rads

[SeanCo]

Good Evening

This post is the conclusion to date of two gas fitter visits and an element of self help which have both failed to deal with matters satisfactorily.

I have a Potterton Performa 24 which was playing all sorts of tricks and I had the PCB and a couple of microswitches replaced some 3 months ago. Within a couple of days it reverted to one of its previous faults, when the HW was fired it was also feeding the radiators. The gas fitter said the diverter valve itself was fine at the time and the PCB was the issue. Prior to this, I had the diaphragm replaced a year ago by a GS qualified family friend who was fortunately in the area, but it didn't help and he advised me to replace the diverter.

Just this week, the boiler has started cutting out when either HW or CH are operated. Initially the boiler fires for some 2 minutes before cutting out and then fires up again within 10 seconds. It then repeats this cycle albeit at reduced 30 second intervals.

I took the DHW heat exchanger out tonight, cleaned it with domestic descaler and rinsed for a couple of hours before refitting. Unfortunately this did not work. No issues with pressure, a steady 1.5 bar. The heating outflow 22mm pipe on the far left does get hot. No warning lights.

I noticed that the top chamber of the heat exchanger is coated with a black almost carbon like substance, but not blocked. Some of this came out when I cleaned it, but a coating still remained. Is this a red herring or should I do the job again using something like Fernox F3?

Whilst I'm at it I'm tempted to tackle the diverter as well. This is effectively two separate components on the Performa 24. Do I need to replace both? This may even be the root cause of everything?

Any pointers or even alternative suggestions would be gratefully appreciated.

 

[twgas]

It certainly sounds like your diverter needs some attention. It's probably full of sludge, along with the system - do you have plastic pipe on the heating circuit?
The combustion chamber needs the attention of a gas man, to clean then check seals, emisions.......

 

[SeanCo]

It certainly sounds like your diverter needs some attention. It's probably full of sludge, along with the system - do you have plastic pipe on the heating circuit?
The combustion chamber needs the attention of a gas man, to clean then check seals, emisions.......

This confirms that it's likely the diverter is shot as I was starting to suspect.

When I drained the boiler the other day there didn't seem to be an inordinate amount of crud.

All the workings of the combustion chamber were checked by the GS fitter I had round 3 months ago. Apart from a minor issue with the flue which took 5 minutes to resolve, a totally clean bill of health on emissions, seals etc.

Now to move on to buying and fitting a replacement diverter. Apart from the obvious like protecting the electrics and photographing it all before starting is there anything else useful to know that's not in the manufacturers instructions?

Thanks

S

 

[SeanCo]

A brief update...

Changed the diaphragm and checked out the diverter. No obvious issues as it appears the pin from the diaphragm is properly engaging when the water is fired up.

Unfortunately it still cuts out (both CH and DHW) every 30 seconds or so regardless.

Should I go back to the to the DHW HE as probable root cause and give it a good chemical clean or is there another more likely possibility?

 

[Terry7556]

a good chemical clean of the dhw he will do no harm at all, it may be a big help but i dont think its the only issue you have
search on here for cleaning plate heat exchangers using chemicals like spirit of salts, fx2? or ds 40 ?
not sure of the correct name of the last two as i tend to go for spirit of salts
just read your last post
the heat is building up and not getting away, boiler senses this heat build up and cuts out until cooler
the he clean should help

 

[SeanCo]

I took out the DHW HE and gave it an hour soaking in a hot citric acid solution and agitated regularly. Unfortunately still the same, both CH and HW are cutting out after a minute or so when cold and then after less than 10 seconds thereafter. The other anomaly I have just noticed is the when the boiler is set to HW only, it doesn't fire when the tap is turned on. Only if CH/HW is on.

Also whilst everything was opened I also checked the overheat thermostat. No issues, continuity fine.

Is it still possible that a completely shot divertor valve is the cause of all this or is it that old favourite the PCB again? If it is the latter at least its still under warranty as I had it changed 3 months ago.

Does anybody have any further possibilities / clues?


Thanks

 

[Terry7556]

yes stop using chemicals that wont do the job
go on ebay, or local if you have a supplier near, buy some spirits of salt and clean the he with that.
follow the safety instructions
you say the boiler does not recognize a demand for DHW on its own, has this always been the case?look at what happens when it fires with ch on, i mean at the diverter valve.does a small pin move to make a microswitch and does this happen (pin moving)on a dhw demand on its own

 

[SeanCo]

OK an update:

Cleaned the DHW HE with 1:2 Spirits Of Salts and Water as suggested. All traces of oxide are gone from visible areas.

HW is now kicking in when the control is set to HW only and the diverter pin engaging. No overflow into CH. HW flow in general also seems better.

I suspect (and are quite happy to be proven wrong) that the diverter was playing tricks due to a clogged up HE?

However for both CE and HW, the boiler is still cutting out every 10 seconds or so. So what next?

MI says either Flame Sensing Electrode (obviously RGI work) or PCB in the case of the flame cutting out, but I'm not 100% convinced. There is a feint 'woosh' before the flame cuts out. Not sure if this is relevant or not?

 

[gas112]

Change the main sensor (ch) its on left hand side in a dry pocket when this is feked it causes cycling as you describe.
And there is no need to change divertor on these just strip it out and clean and grease the pin in back section it is the tiniest coating of crude on it stopping it moving properly

 

[SeanCo]

Change the main sensor (ch) its on left hand side in a dry pocket when this is feked it causes cycling as you describe.
And there is no need to change divertor on these just strip it out and clean and grease the pin in back section it is the tiniest coating of crude on it stopping it moving properly

Thanks this seems entirely plausible. The part has been ordered.

 

[SeanCo]

Change the main sensor (ch) its on left hand side in a dry pocket when this is feked it causes cycling as you describe.
And there is no need to change divertor on these just strip it out and clean and grease the pin in back section it is the tiniest coating of crude on it stopping it moving properly

OK I have done as suggested and changed the sensor, it was very straightforward, but unfortunately the cycling continues.

Does anybody have any further suggestions?

 

[SeanCo]

I really am still scratching my head on this one. No issues with flow whatsoever which virtually eliminates blockages as the cause. Maybe what I mentioned previously is the next logical step?

MI says either Flame Sensing Electrode (obviously RGI work) or PCB in the case of the flame cutting out, but I'm not 100% convinced. There is a feint 'woosh' before the flame cuts out. Not sure if this is relevant or not?

 

[Gasguru]

Cycling on/off can also be due to airflow sensing issues...rgi work.

 

[Aquilani]

Doesn't this boiler have a filter incorporated in the return isolation valve which can become blocked?

 

[SeanCo]

Doesn't this boiler have a filter incorporated in the return isolation valve which can become blocked?

I have done a search it appears that it indeed can happen. The MI only talks about the Cold Water Inlet Tap Filter. I presume the process of cleaning is the same?