Rayburn 368k explosive ignition

[JLS]

God how I hate this thing! So the problem with this thing aside from it being filthy and inefficient is that the boiler keeps cycling and on restarting has an explosive ignition. I've checked and rechecked the levels of the boiler burner, flushed the central heating pipes and all the rads and tried different pump speeds all to no avail. The system only has three radiators on it at the moment and the temperature difference between the flow and return appears to be in spec when measured with a laser thermometer directed at the pipes. The fan also runs for the specified time after shut down before the re ignition sequence starts. My guess is that the boiler runs, reaches overheat and shuts down but as the stat is still calling for heat. it fires up again. fuel is introduced into the burner that is still too warm, vaporizes and explodes. I have no idea on how to stop this and every engineer I've talked to has been equally clueless so if anyone has some input it would be very gratefully received. Failing that I wonder if someone could clear up the exact intended process of the start sequence for me. Specifically with regards to the pilot light reservoir, as I understand it the glowplug is activated (after fan and thermocouple check etc) followed by the pilot solenoid which fills the pilot reservoir,soaks the wick and the wick is ignited by the glowplug. Is the idea that the pilot reservoir then overflows into the main boiler or is it contained until the main boiler fills to the same level and ignites at that point?
Thanks for reading

 

[SJB060685]

You'll find it hard to find a decent engineer who either knows there stuff about the Nouvelle range, or is prepared to work on one.
Short ignition sequence is.
Demand for heat.
Fan runs and air switch proves fan is running and chamber is sealed.
Pilot solenoid opens.
Ignition comes on.
Thermocouple detects heat.
Pilot solenoid closes and main burner solenoid opens and glow plug de energises.

I can't be any more specific on that at the moment as my work iPad with my manuals is charging up at the moment.
Google 368k service manual and read through the sequence there. Failing that I could probably upload the file tomorrow.

If the overheat stat trips out then the boiler should not attempt a restart until manual reset.
It's possible one of your solenoids is letting by, causing the explosive ignition.

 

[SJB060685]

Note. Doesn't appear to be an overheat stat

 

[JLS]

View attachment 64188

Note. Doesn't appear to be an overheat stat

Sorry I probably used the wrong terminology. What I meant was that the boiler thermostat cuts in and kills the boiler. I spent the day working on the evil thing. Even went as far as verifying the ignition sequence visually by leaving the burner baffles and thermal blocks out and it all checks out. Neither solenoid is letting by and having watched it all happen I can't really see how it could have an explosive ignition. Yet when it's cycling and already hot there's a distinct "whoomph" on ignition which I don't believe is there when it's cold. The boiler has been off all summer so it's not fresh in my memory. The baffles are also getting destroyed, particularly the upper one. I managed to find some second hand ones last year but the upper one is already knackered. cracked in 3 out of 4 bridging points and the central gap almost completely closed up. With a replacement North of £130 it's going to meet the big hammer and the welder tomorrow! The only other thing that I could find that was out of spec was the main boiler feed which was somewhat less than it should have been but by the time that comes into play the pilot reservoir has already spilled burning fuel into the main chamber so it's hard to see that being the source of the trouble.

 

[SJB060685]

Many consider these units archaic pieces of c#@p, in fact most of my associates in the oil industry outright refuse to touch them. Are you saying the baffles are warped and potentially affecting the flue draft? Are you certain this only happens when hot and relighting?
Is this a problem that's only just started, or has always happened and you're only just noticing it?

 

[exedon2]

As SJB060685 say this cooker was always a lump of crap .
I've a full time oil service engineer but we refuse to service them, life's too short to battle with them!
Back in the day did convert a few to pj anyone still make a conversion kit?

 

[SJB060685]

As SJB060685 say this cooker was always a lump of crap .
I've a full time oil service engineer but we refuse to service them, life's too short to battle with them!
Back in the day did convert a few to pj anyone still make a conversion kit?

That I couldn't say mate. We had several Nouvelle's on our books, unfortunately the last time I even saw one was when I was an apprentice about 20 years ago and the old man always did the work on them. My dad passed away a few years ago though so I can't even ask his thoughts on the matter.

Has the OP checked the oil level of the boiler burner?

 

[JLS]

Those that think that way are absolutely right, they are archaic piles of crap and I would have thought not seeing one in 20 years should be considered a blessing. Yes the baffles are warped but affecting the flue draft suggests a level of sophistication that I suspect is highly unwarranted. Being a bit more serious about it I don't think it's causing a problem as we get no smell of fumes and neither of the two CO alarms register anything untoward. That said it doesn't sit right with me putting them back as they are so I will attempt to restore them and if that doesn't work I'll have to shell out for a new one. Yes I did recheck the burner oil level and it's sitting at 15mm which is the lower end of the limit but in spec. As for whether it only happens when hot I cannot be 100% sure but I believe so. I'll take particular note when I fire it up again later

 

[SJB060685]

15-17mm is what the manual suggests if I remember correctly yes.

 

[JLS]

Impressive, you're spot on

 

[Lecyviolin]

On this subject where is the wick situated? I can not find any pictures or diagrams just a mention that it should not touch the glowplug. The wick has vanished from my boiler!

 

[JLS]

When you take the boiler burner out and remove all the baffles, you'll see the end of the glowplug sitting in a small reservoir. That reservoir has a small dividing wall and the wick should be draped over that. They can get pretty cruddy and may no longer resemble a wick but if it truly has vanished I would have thought your boiler would be locking out. That said a vanishing wick is one fault ours hasn't come up with yet so I won't swear to that.