Potterton Netaheat 10/16 boiler not firing up

[andycad]

I have a Potterton Netaheat 10/16, with a main burner that won't fire up. I've dismantled and cleaned the burner to no avail.
The thing I've noticed is that even though the pilot light lights, there is still a small spark from the electrode, which is within the flame, and a corresponding one in the electronic control box, every second.

According to the fault finding chart in the manual, it suggests that if the spark doesn't stop ' does pilot flame engulf electrode?' (which it seems to - flame is about 1 cm square), and if it does ' is electrode or lead faulty?' .
From my understanding, it's the electrode that lights the pilot so if the pilot lights why should the electrode or lead be faulty? And how should I test for any fault in the electrode or lead?

 

[Agile]

This is a positive case pressure boiler.

They can be very dangerous for DIY working. Consequently I am not going to give you further advice apart from to get a registered engineer!

The flame detection is by the same electrode. At the ignition voltage of 14 kV it will spark across a small gap with no obvious effect.

The flame detection only uses about 150v and this needs a low resistance path back to the PCB.

To check the electrode and lead a conductivity test is needed from the tip of the electrode back to the PCB.

However, I cannot encourage you to do this for safety reasons as it involves opening the combustion chamber case..

Tony

 

[andycad]

Agile - thank you for your speedy reply. I take on board your advice regarding a registered engineer, but unfortunately the only one I know and trust is on holiday at the moment.
So, as I understand it the flame should be detected by the electrode which sends a signal back to the electronic control box which is weaker than the spark and therefore more susceptible to being affected by a poor connection, so i'll test for resistance with a multimeter, having disconnected the gas and electric supply.

But what I don't understand is how that would affect the ignition of the main burner. Does the electronic control box think that there is no flame, and therefore it isn't allowing gas to the burner?

 

[namsag]

Yes it thinks pilot has not established , cracked electrode, loose lead . too small a pilot will all stop correct signal going back

 

[gassafeman]

This is a positive case pressure boiler.

They can be very dangerous for DIY working. Consequently I am not going to give you further advice apart from to get a registered engineer!

The flame detection is by the same electrode. At the ignition voltage of 14 kV it will spark across a small gap with no obvious effect.

The flame detection only uses about 150v and this needs a low resistance path back to the PCB.

To check the electrode and lead a conductivity test is needed from the tip of the electrode back to the PCB.

However, I cannot encourage you to do this for safety reasons as it involves opening the combustion chamber case..

Tony

I see some members still continue to give advice on Boilers, and Positive pressure at that. I guess it makes them feel better and boosts their ego.

Paul

 

[namsag]

You missing something gassafeman its called DIYnot. com
Agile had already told him what it was .
IF you dont want to give advice then dont. simple

 

[andycad]

Thanks for your help Agile and namsag. it's a shame that you've been criticised for giving advice in the spirit of the forum. In the absence of any advice I would have suspected a gas supply fault, and in troubleshooting, probably done far riskier things than than simple circuit testing, and rectifying, when the appliance is switched off. I'll look at it tomorrow and report back.

 

[tonybhoy]

Thanks for your help Agile and namsag. it's a shame that you've been criticised for giving advice in the spirit of the forum. In the absence of any advice I would have suspected a gas supply fault, and in troubleshooting, probably done far riskier things than than simple circuit testing, and rectifying, when the appliance is switched off. I'll look at it tomorrow and report back.

Hope you know what your doing with that boiler casing. The advice you've been given above is really questionable IMO.

To reiterate that boiler is a positive fanned boiler and if you don't know the implication of what that means then you should leave well alone, but your call......

 

[Agile]

Its not totally clear if anyone has criticised me.

The advice I gave was very clear and indeed in bold to get a registered engineer.

I did go on to explain some of the technical aspects involved, NOT to encourage you to do it yourself but to help you understand whats going on.

Just to rub in the safety aspects I ended by saying that I cannot encourage you to do any of these things yourself.

At the end of the day its your boiler and your life at risk. I suppose your life may not be very important but there may be parents, wives, children or neighbours who are totally innocent and who could be killed or injured by your desire to save a few pounds.

If it was going to save some bodies life then I would go and fix a problematic boiler free of charge! But perhaps I am a little oversensitive about these things at the moment because a very active lady I know is in hospital with only a few days to live as she has multiple cancers. Three weeks ago she was at work in the same hospital! ( Royal Free ). She is totally mentally alert and I am trying to pluck up courage to go and visit her. A friend of mine went last week and said he may come again this week, she replied "well telephone first to make sure that I am still here!"

Tony

 

[gassafeman]

Tony,

I personally think if your not going to give advice then dont, full stop. Im sure your educated enough to know that. You explain that the boiler owner needs an RGI, and then explain what you would do to ascertain what is wrong. Its a blatant contradition. The boiler owner will now act on your posting, whether you call it advice or not - you have now educated him / her after all.

I have been lambasted by you for advising how to test a solenoid and you giving advice on a positive pressure boiler albeit hiding behind the phrase 'I advise an RGI' does not wash.

We all know you are a boiler expert, and your advise in the CC is 2nd to none (and thats from personal experience).

The likes of namsag dont care who they give advise to, will do cheap jobs for 'beer money' based on assumptions, and make a mockery of decent engineers who try to earn a wage. Why stoop to their level?

Paul

 

[andycad]

Thanks to everyone for advice. I bought a new electrode and lead and fitted them yesterday, but still the same spark every second even though the pilot flame is lit, and the electrode glows red hot.
With the boiler on I also tested the output voltage to the gas valve (something mentioned in the faultfinding guide in the manual), and this was zero, so I think that indicates that the PCB needs replacing, rather than the gas valve (which has apparently been discontinued anyway).

This seems to be a controversial issue. The issue of whether I should be given advice on anything that involves removing the casing is, in this case, academic, since I had already removed the casing, before I posted on this forum. Thanks to advice given on this forum, what I originally had thought to be a gas supply problem, seems to now be a PCB fault which won't involve any further removal of the casing.

It's been mentioned more than once that this is a positive case pressure boiler. By using Google I found out that this meant great care needed to be taken when refitting the casing that there was no leakage from the case to the room. Those criticising others for giving me advice could have perhaps used their energies better to advise me the importance of that.

Agile/Tony - very sad to hear about your friend in hospital. I hope you manage to visit her while you can, and thank you again for your advice.

Namsag - you seem to have attracted harsher criticism here, which seems unwarranted on the basis of advice that was clear and concise and complemented Agiles, which was more technical in nature. Thanks.

 

[Agile]

My advice is usually more technical in its nature.

When you first posted, I was faced with the situation that you had already opened the combustion chamber. Nevertheless I still advised you of the dangers involved and recommended a gas registered engineer.

However, as you seemed to have an appreciation of some of the electronics I decided to give you further information on how it works. That was not intended to encourage you to do any further work although I was aware that if you did then it would focus your attention away from the gas valve and onto what might be involved.

I never encourage DIY work on GAS or dangerous boilers !

The flame detection is made from the "earthy" end of the HT transformer. If you can identify that there is usually a high value resistor of about 1 Meg in series and that may have gone open circuit.

I am not encouraging you to fiddle with the PCB but if you are going to then thats what might have failed.

I welcome Paul criticising me for giving some of the advice in this instance. It helps to reinforce the safety issues and also comments on some of the people on this forum who post totally inappropriate advice to encourage unqualified gas work. They post here without giving their names of course.

Tony

 

[andycad]

Thanks for the further advice, Agile.
I thought I should mention that I did read on a website about this boiler-

"Common faults are fan failure, control board failure, erosion of the earth electrode on the pilot ignition"

The earth electrode is no longer the rectangular shape shown in the diagram, so has presumably eroded to a more crescent shape along one side, with a point. The distance between it and the electrode, about 2 to 3 mm, is correct and it's obviously sparking alright. Is there a chance that replacing the earth electrode, could solve the problem?, before I enter into contemplating £100 + on a new PCB, although I will look into testing the resistors before I do so.

 

[andycad]

problem solved - it was the PCB. I managed to get a secondhand one on eBay for £22. Thanks to everyone for their help.