Pilot Light Problems

[BillPl]

I have a Myson boiler on which the pilot light goes out once central heating has been running for 1 hour +.
So far I have had new pump fitted, new 3 way valve fitted, new thermocouple fitted, new over run controller fitted and new room thermostat fitted. However pilot light continues to go out.
I am getting hot water and central heating is working, radiators seem to get very hot and after about 45mins to and hour boiler shutsdown and extinguishes the pilot light. Engineers have now made 4 visits but I'm no further forward, but poorer, any ideas !

 

[ChrisR]

What's the boiler? Model and output please?
Could be blocked pilot, faulty boiler/overheat stat, gas rate, connections ....
Do you have TRV's on all your rads?
Do all the rads get to the same temperature?
What speed is the pump on?
Does it go out quicker if the boiler stat is turned up?

 

[BillPl]

Thanks for the reply
What's the boiler? Model and output please?
Myson Apollo, output don't know, currently at work will advise when get home
Could be blocked pilot, faulty boiler/overheat stat, gas rate, connections ....
Do you have TRV's on all your rads?
No
Do all the rads get to the same temperature?
Generally yes, 1 slightly colder but no so much
What speed is the pump on?
How do I check, what should it be?
Does it go out quicker if the boiler stat is turned up?
All depends on boiler start temp, if boiler already warm pilot goes out quickly after switching on, if starting from cold appears to take longer to cut out, but never measured the time

 

[BillPl]

Pump is on max speed, turned it down and no difference pilot light still goes out but this time radiators did not get so hot

 

[ChrisR]

I'd
check/replace boiler thermostats (3 on some models)
(and mebbe suspect sludge/scale in heat exchanger and/or system.)

 

[BillPl]

Once again thanks for the reply

Apparently there are 4 thermostats! What do I need to do to check for sludge etc and how do I clean? Don't know the history of the boiler as just moved in to this house.

For sure pilot light going out everytime now once either hot water or central heating on for 30mins or so and pilot light won't relight until boiler stands for a while, I guess cooling down. Does this support your thoughts on reasons why?

 

[namsag]

You have already had the pump over run stat changed, And the overheat stat appears to be doing it`s job. So that leaves just the Hi an Lo stats to be changed. For all they cost and little additional time to fit just renew both.

 

[BillPl]

Thanks for the info, will have these changed. Soon will have whole new system !
With regard to sludge etc blocking up the heat exchangers how can I check this is not a problem and how do you prevent it becoming a problem? Perhaps a basic question but I am learning fast and thanks for the support folks

 

[BillPl]

Well hi and low thermostats now replaced and no better !

Pilot light goes out once boiler gets too hot. I can get hot water because water gets hot enough before boiler overheats. But with the central heating it takes longer to get house upto temperature (21C) and boiler gets too hot knocking out the pilot light. My latest engineer says sludge may be in the system but slow flow should not lead to boiler overheat as the thermostats should control.

So main pump, 3 way valve, room thermostat, thermocouple and wires, pump overrun, and high + low thermostats replaced ! Pilot light still being knocked out !

Help

 

[Agile]

If you had really exhausted every eventuality then there is only one cause left and thats the gas valve sticking on!

However thats very unusual and I would suspect the system flow due to pump or sludge. A somewhat slow flow should not present a problem to the boiler but if its less than about 60% its unlikely to be able to control itself properly.

I would test the flow by measuring the differential temperature across the heat exchanger.

Tony Glazier

 

[ChrisR]

And the overheat stat appears to be doing it`s job.

Well maybe not - if it's too keen to see an overheat, the pilot WILL go out!
Now we said check three!

 

[BillPl]

If sludge is a problem and slow flow would I not expect to see radiators not heating up very well? They do get very hot and distribution is OK (all radiators are heating) would this not suggest pump and flow is OK. Pump has been replaced (although last engineer did comment it seemed quiet, but said may just because of efficient system).

 

[Agile]

When we talk about the "pump" what we really mean is the "pump function" that is of providing a flow.

Even though the pump may be fine we sometimes find the pump isolating valve is blocked or not opening fully. To an engineer that is a faulty pump function even though the pump itself may be OK.

Until the temperature differentials have been measured I will continue to suspect the flow through the boiler is too low. If it turns out to be satisfactory then I will look elsewhere. I dont speculate, I just test everything in a logical order.

Clearly you have had some pretty incompetent people attending and I would not trust them to have carried out even the most basic preliminary tests like the boiler burner pressure and/or gas rate. It sounds as if they were just "parts changers". They did not deserve to get paid as they did not solve the problem.

You have to realise that I cannot rely on your idea that the flow rate may be good. There is a fault and I need actual measurements to give me any opportunity to diagnose the fault.

Tony

 

[BillPl]

Tony

You mention

Until the temperature differentials have been measured

What exactly do you mean by this, inward and outward temp of flow into the boiler? How should this be measured. Sorry for so many basic questions but I you can guess I ain't an engineer.

Your right so far I've had 4 visits, 3 engineers and they just seem to "guess" which part is next most likely to be the problem and replace it.
Last two guys I haven't paid, but suspect when / if they do fix it they'll tell me all the other parts really did need replacing and I need to cough up for the lot, even if its the last part that does the trick.

Just heard engineer 4, visit 5 is on Thursday. What tests and values should he be measuring?

 

[Agile]

There are parts changers and engineers.

Its obvious what the parts changers do, change parts!

The engineer will assess to operating parameters of the boiler and deduce from the measurements what the fault is likely to be.

Your boiler is designed for a differential of 11 C. This is the product of the heating power input to the boiler as set by the gas burner pressure and the flow rate of the water through the boiler.

Any competent boiler engineer will have a digital contact thermometer, the better with two sensors which are each connected to boiler inlet an doutlet and they can measure the temperature of each sensor or the difference between them.

If the flow is too low the temperature differential will be too high and the boiler cannot be expected to control its temperature as designed.

Tony Glazier