Potterton Puma 80 perm pilot light switches off

[ChrisR]

Good, we're getting there!
Ok next thing is to measure the gas rate on CH, that's how much gas is being used. Do it at the meter, as in the FAQ wot I rote. I can't remember the low rate offhand, but it should be a lot lower than the 27kW or so it could be if it's wrong.

Also, if you put the CH on , from cold, how long does it take for the return pipe connection to get very hot, and are any/many of the rads hot at the same time? I'm still suspicious of the flow rate being too low.

If the gas rate is wrong, it's not a diy job - you need the right kit and to know how to use it.

 

[pennib]

Thanks Tony,

Can you explain why the burner pressure is OK for the DHW but not for the CH. Are the minimum and maximum gas pressures the same for both systems? If so why will the DHW work but not the CH?

Confused by Combi
Neil

 

[pennib]

Thanks ChrisR,

I have a metric gas meter, it uses 0.051 cubic meters every 2mins when CH is working, which is 16.371 Kw as per your calculation.

I have timed the CH Return pipe getting hot at 3mins approx, but the radiators are not uniformly hot, in this time. I will have to double check that I have bled the rads enough.

The CH is locking out at 7-8 mins from a cold start.
If I try to restart the CH immediately after lock out the boiler will Lockout again under 1 minute.

Thanks for your help on this
Neil

 

[Agile]

That proves what I have been saying that the gas valve needs setting up by a competent CORGI !

Hot water needs the whole boiler power of 24 kW output but the CH only needs a very small amount of power, perhaps 5-8 kW.

If your rads are not warming up at the same speeds then they need balancing! See FAQ.

Tony

 

[pennib]

Hi Tony,

Is the gas rate wrong?

Neil

 

[Gasguru]

Does the system have a bypass? and if it does is it sufficiently open?

 

[pennib]

Hi Gasguru,

Yes, how do I check that its sufficiently open? The manual says. "Note: if the by-pass flow is restricted too much this will cause the appliance to overheat and go to lockout". Which is what seems to be happening

If I turn the hexagonal allen key anti clockwise on the DHW Manual Flow Restrictor, I presume this will increase the flow. How do I measure this flow rate? or is it trial and error?

Is it by running a hot tap and timing how long it takes to fill a pint glass then after adjusting the 'Restrictor' taking another timing?
I don't know what the system volume is.

 

[pennib]

On second thoughts I'am now not sure. The manual says there should be one, and there is this Hexagaonal Allen key with a c. clip below it. Is this it?
The description part says " DHW Thermostat/Flow Limiter Assembly. So it must limit flow, but I can't turn this allen key.

Can any one advise please

 

[Agile]

Leave it alone! Its nothing to do with CH !

The minimum gas rate setting is a long way out and needs a competent corgi to reset it. Only some can do that!

However, although a contributory factor it may not be the full story.

There is a rare PCB fault that catches many engineers out! When the boiler modulates down to minimum, if the flow temp still gets too high then the PCB should turn off the gas to the burner. Thats a seperate part of the circuitry on the PCB.

Sometimes a PCB fault does not do that. That might be the problem in your case although until the boiler is set up correctly we cannot come to any conclusion.

Tony

 

[pennib]

Thanks Tony,
You say, "The minimum gas rate setting is a long way out and needs a competent corgi to reset it. Only some can do that!"
Can you suggest someone?
London, Wandsworth SW18
Neil

 

[Agile]

Chris R is not two million miles away, nor is Gasguru.

Either of them will be able to set up the gas valve and if that does not solve the problem to identify what else is wrong.

The overheat stat on that model sometimes ages and trips at a lower temperature and that may also be at fault so they would need to bring one with them and measure the tripping temperature.

Tony

 

[pennib]

Thanks Tony,

Can I have ChrisR's and Gasguru contact numbers or email links please.

Thanks everyone for all your assistance, its much appreciated

Neil

 

[Agile]

You have to look in their profiles!

But a good start is to put YOUR contact details in your profile first!

Tony

 

[ChrisR]

I have a metric gas meter, it uses 0.051 cubic meters every 2mins when CH is working, which is 16.371 Kw as per your calculation.

That proves what I have been saying that the gas valve needs setting up by a competent CORGI !

No Tony, the minimum you can set on the CH is about 17kw, so it's spot on.

Hot water needs the whole boiler power of 24 kW output but the CH only needs a very small amount of power, perhaps 5-8 kW.

Sure, so the burner should turn off, as you say.

 

[Agile]

I am very surprised if the max/min CH is 24/17 kW but there are no tame Pumas that I can think of very close by for me to test.

Well there is one but its been stupidly boxed in.

If that is true then it would need a thermal survey to see if the o/h stat is tripping below the set value.

If not then the PCB is at fault but I dont encounter that fault very often on Pumas and the PCB is only two years old ( although that proves nothing ).

Tony