potterton puma 80 ?overheating problems

[muppster]

Hi can anyone help me???

I have a fairly well used potterton puma which seems to have adopted this dreaded overheat cut out problem they tend to develop. I had a plummer out who replaced the thermocouple and overheat stat - no joy, I replaced the flow microswitch which was sticking slightly and also the automatic air vent which was leaking, but still have problems.

The boiler works fine if it's just central heating, or domestic hot water you're after on their own. The problem is that if the central heating is running and then hot water is used for a prolonged period (ie to run a bath while central heating is switched on) the boiler cuts out on turning off the tap. It always lights easily afterwards, but does require manual re-lighting. It's definitely not the flow switch, flu, pilot, thermocouple, fan, overheat stat, or pump so to be honest I am left wondering what the hell it could be?????

All other times it works fine it's just in this particular instance.
Any help would be greatly appreciated.

 

[gaspro1981]

no offence but how do you know that it is not one of the above mentioned parts

 

[Agile]

What does the "plummer" have to say?

Is he Gas Safe registered?

Tony

 

[muppster]

yes he is gas safe - he's not sure what else it might be but seemed to think that it would start to get expensive to replace further bits and since the boiler works alright most of the time I shouldn't bother. I just don't like to leave something that is not working 100% and wondered if anyone else had come across anything similar? It is quite distinct in that it only cuts out when I use hot water for a prolonged time with the central heating on.

As to the other reply, the plummer seemed to think that the pump, flu and fan were okay, the pilot is fine, the thermocouple is new as is the overheat stat and flow microswitch so I doubt it's them.

Any more ideas anyone????

 

[Agile]

I would generally agree with him that its not exactly any one of those parts at fault.

The problem is likely to be related to how they are controlled and interrelate together.

Tony

 

[bengasman]

Simple, get a better plumber.

 

[baxpoti]

Check the dhw flow switch operates the microswitch correcttly.
What distance did you set the microswitch up to?

Has the high gas burner pressure been checked?

 

[muppster]

thanks bengasman, very helpful indeed! As you say, Pay peanuts expect monkeys, it seems you also think, pay nothing and expect a stupid comment.

 

[bengasman]

Was not meant as a joke or silly comment.

Puma's are fairly simple boilers and the chap that has been experimenting on it shows questionable knowledge.
Some of the basic things you check when overheat occurs repeatedly are burner pressure and gasrate, neither of which are mentioned.
It is also known that puma's suffer more from soiled systems than other similar boilers and nothing indicates that he checked for problems caused by corrosion/limescale, even though a faulty aav is often an indicator as is the sticky switch.
And the fact that you, who is paying him, are now trying to find the answer for him seems to show that you don't have too much confidence in his abilities either.

 

[Agile]

So you see that we all agree that you need a more skilled person.

I would suggest a boiler engineer rather than a "plummer".

You need someone who really understands exactly how boilers, and particularly this one, really work.

Tony

 

[weargas]

quite simple, when the hot water tap is turned off the pin isn't moving back fully so it's staying in dhw mode with the tap off. Bang, clatter, overheat. The clues were in the first post. Get your plummer to see if the red light on the pcb stays on after the tap is switched off. If so it could just be a case of removing the pin from the diaphragm section (water off and dhw drianed), cleaning and greasing it so it moves freely.

 

[Agile]

Did he measure the cold resistance of the CH temperature sensor?

If thats high then it can leave the boiler on full power during the time that the diverter valve is not yet open to the CH system.

Tony

 

[gazdaz36]

Hey muppster dont listen to these clowns on here your problem is the wax valve diverter when you turn tap off the diverter is too slow to open up the heating circuit therefore boiler cant "dump" excess heat into the radiators causing your overheat problem

 

[Soggy_weetabix]

Hey muppster dont listen to these clowns on here your problem is the wax valve diverter when you turn tap off the diverter is too slow to open up the heating circuit therefore boiler cant "dump" excess heat into the radiators causing your overheat problem

Do listen. gazdaz36 seems not to understand the boiler fully and seems to think a wax capsule will cure any over heat faults. Never have I came across overheating when delivering hot water due to a wax capsule. I personally suspect the water section at fault. Weargas has explained it.

David

 

[gazdaz36]

Hey muppster dont listen to these clowns on here your problem is the wax valve diverter when you turn tap off the diverter is too slow to open up the heating circuit therefore boiler cant "dump" excess heat into the radiators causing your overheat problem

Do listen. gazdaz36 seems not to understand the boiler fully and seems to think a wax capsule will cure any over heat faults. Never have I came across overheating when delivering hot water due to a wax capsule. I personally suspect the water section at fault. Weargas has explained it.

David

obviously you have never worked on these boilers before and clearly dont understand how they work i've only been repairing heating and boilers for over 15 years many of which for bg and now work for boiler manufacturer and i'm very good at what i do trust me