Potterton Promax 24HE Explosive Ignition

[DJNelsonHeating]

Hi. If anyone can help me try and pin down an issue with a customer's Potterton Promax 24HE...

I was called out to this just before New Year, as it had literally exploded (well, the burner anyway), and scared the living daylights out of the occupants who thought the front door was being kicked in! It had the old fabric type burner, which was quite dirty and clogged, and clearly the offending part. I duly replaced the damaged burner with the new ceramic type burner and also fitted the new injector pipe that was supplied with the burner. The boiler fired OK, and I left the customers with a perfectly working, serviced boiler.

However, this week I was called back, as it had worked fine for a month or two, but then started to make explosive ignition noises again, getting worse over time. I again inspected, and the burner I had installed was fine, but the electrodes were 'bent' downwards slightly, so not at 90 degrees like the sensing probe. I set these straight, at right angles to the door and set the gap, thinking that was likely the issue.

I then carried on with all my other checks - gas rate (2.33 m3h compared to 2.31 stated in the manual, so fine), fga (fine 0.0006), inlet gas pressure at gas valve (18.5mb - manual states 18.1 to 22.5, so fine I presume for the boiler to work, depsite the drop being 2.5mb (working pressure at meter was 21mb)), etc.

All looked good visually and by readings, etc.

Just before leaving it cycled back on and made (a small, admittedly) a larger than usual ignition bang, which I couldn't get it to do again. The customer DID state the explosive ignition was very intermittent, so unsure if the electrode's setting has fixed it 100%, especially as I had one loud start while I was there.

I have asked them to let me know if it continues to do it, or if fixed, but in anticipation of a call back, and me scratching my head looking befuddled, does anyone know of any other reasons why this could be happening? I understand from forums that the Promax seems prone to it, but that doesn't fix it, or allay the customer's fears of exploding boiler! I had thought the ignition PCB, but I am admittedly clutching at straws with that and don't want to replace parts that don't need it!

Many thanx in advance.

 

[galaxy_plumbing]

Do you get spark before gas? It seems to me like some gas accumulate in the burner before pcb sends voltage out. Just a guess, will see what more experienced guys say

 

[DJNelsonHeating]

The boiler fan runs, then there is the tell-tale 'click-click-click-whoomph', though you can't see the spark through the burner 'window'. Sometimes it ignites after a few clicks, other times after a single click. Makes sense that perhaps the ignition pcb is 'late' with spark, but I don't have anything definitive that would say that - it's just my next logical port of call, hence why I was hoping someone here would have experience of this.

 

[Syty]

Could it be Ignition PCB?
Lack of air for combustion?
Ignition Electrodes? spark gap should be 4mm

 

[diamondgas]

Replace the electrode's would be my first port of call then the spk gen if that doesn't resolve it ... also check out the earths ... You got to remember that the mixture entering the burner chamber is much more volatile and enclosed than more conventional boilers. The longer it takes to ignite the bigger the bang

 

[galaxy_plumbing]

Good thinking diamondgas. I was just thinking about loose earth cable.

 

[diamondgas]

So do you sometimes actually get correct ignition on first spark?

Never counted

 

[galaxy_plumbing]

I meant in DJ's case

 

[diamondgas]

I meant in DJ's case

This forum takes some getting use to ... Personally I like to see the flame first time ... I wouldn't like to count the frequency to be honest as they're a rapid spark with forced draught burners

 

[mfgs]

The electrodes on these can be troublesome, I'm pretty sure they changed the design due to soo many problems and the new ones are better.

 

[Billy Bob Bob]

i would agree with Steve the electrodes would be my first thoughts as well and they are prone to problems on this boiler

 

[DJNelsonHeating]

I do believe the electrodes (the whole combustion box door panel with electrodes sticking out of it) were changed prior to my seeing it for the initial exploded burner.

The customer had the 'old' combustion box door panel on one side, explaining that their previous engineer had changed it.

Are there any particular checks I can run on the electrodes to 'prove' they are good, etc?

 

[Billy Bob Bob]

I do believe the electrodes (the whole combustion box door panel with electrodes sticking out of it) were changed prior to my seeing it for the initial exploded burner.

The customer had the 'old' combustion box door panel on one side, explaining that their previous engineer had changed it.

Are there any particular checks I can run on the electrodes to 'prove' they are good, etc?

not really send a pm to poxi a member on here he can probably give you a better insight into this boiler i avoid the baxi,potterton,main heat onlys at all costs i dont understand why these boilers are still in production

 

[fixter1]

id say electrode,, but have had them where gas valve is passing

 

[Blumper]

At the risk of appearing dumb if I'm missing something obvious..........and also to change subject slightly...is a 2.5mb drop from the WP to boiler inlet not a bit of a problem in itself, the explosive ignition notwithstanding ?

 

[thomas donovan]

i am dealing with the same boiler similar problem at the moment, while i appreciate all the input from others my mind has been working overtime to solve this problem, my customer has had the odd explosive ignition so i tried to make that happen whilst there as you can imagine it didn't, what did happen though was that it ignited then went out then ignited then went out then stayed alight on the third try. by my reckoning the ignition pcb would control the amount of gas to feed gas valve for ignition and make sure that when ignited the valve would stay open, i have bought an ignition pcb as i am confident that it's where the issue lies i'll let you know how it goes. told customer the boiler was c r a p but being an architect with approx 25 properties in his portfolio he couldn't afford to spend under 1500 quid on a new boiler( including fitting)

 

[mutley racers]

so thomas, was the ignition pcb the fault? I have the same problem with my main 15he. I changed the ignition electrode and checked all earths but still the same bang. Also there is a little black burn mark on the burner where the ignition electrode is. It never lights on the 1st click but always around the 4th. So am interested to see if i need and ignition pcb

 

[thomas donovan]

seemed to have worked with the occasional explosive ignition, but a month later the boiler would periodically stop and need to be reset so disconnected the earth from the condensate trap as advised by the manufacturers haven't heard from the guy since

 

[Bisutommy]

so thomas, was the ignition pcb the fault? I have the same problem with my main 15he. I changed the ignition electrode and checked all earths but still the same bang. Also there is a little black burn mark on the burner where the ignition electrode is. It never lights on the 1st click but always around the 4th. So am interested to see if i need and ignition pcb

Hi
I have the combi boiler Potterton Promax 28 and the same issue it never ignites on the first time and also after it ignites and the water is flowing you can hear the loud bang again occasionally. I called the service man and he checked the boiler and said that is all ok. Only thing that he changed is the ignition electrode because the gap between the electrodes was much more then 4 mm. But the loud bang still remains. The boiler has 4 and half years. Any help much appreciated

 

[Rickster123]

Hi
I have the combi boiler Potterton Promax 28 and the same issue it never ignites on the first time and also after it ignites and the water is flowing you can hear the loud bang again occasionally. I called the service man and he checked the boiler and said that is all ok. Only thing that he changed is the ignition electrode because the gap between the electrodes was much more then 4 mm. But the loud bang still remains. The boiler has 4 and half years. Any help much appreciated

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