Boiler Exploding!!

[DavidW]

Not really, but it sound like it and my wife is worried that it will explode. So here's the story.

My central heating is powered by an Apollo Fanfare boiler which must be nearly 20 years old. During the summer it worked OK - no noises apart from an occasional slight rattle from the radiators when the pump started up.

Now that the winter (??!) has come and it is on almost continuously, it has started playing up. The symptom is a very loud explosive bang which shakes the whole house. It only happens at odd times - no pattern as far as I can see. Sometimes the system will run for several days without anything happen and then twice in a day. It happened this morning, a very loud bang followed quickly by two softer ones.

I have searched this group and others and the general view is that this is caused by over-heating in the heat exchanger, possibly due to the pump not working. The other possibility is that the boiler is not igniting properly so there is a build up of gas in the boiler which the ignites with a bang.

The pumps seems to be working properly as I can hear it when I hold a screwdriver to the case and my ear. However the pump is wired for overrun via a thermostat in the boiler so I thought this could be faulty. How do I check that the pump is running when it should - apart from standing over it for hours on end!

The gas exploding is another matter which I have no intention of fiddling with! Though the pilot light does seem a bit small when viewed throught the window, Is it possible to turn this up a bit?

Hints and suggestions are definitely welcome, particularly on fault finding, as we don't relish the idea of a cold house on Christmas day!!

Thanks

[Andrew Gabriel]

That can certainly be a cause, although I have no experience of that boiler. If it's not catching the gas as soon as it comes out of the main burner, an explosive mixture can build up before it finds the pilot light.

If it's shrunk or changed shape, it needs cleaning. It could well be an indication that the whole boiler needs a clean, as if dirt is building up, it will probably be affecting the main burners too. This is extremely important if that boiler isn't room-sealed. The pilot probabably has a gas adjustment, but you mustn't adjust it until after cleaning the pilot jet/burner (and it probably won't be necessary then).

When it's alight, what to the main burner flames look like (if you can see them)?

[Dave Plowman (News)]

They get partially blocked with crud reducing the flame size. When was it last serviced?

[Doctor Drivel]

My God! This one never had his boiler serviced for 20 years and boasted about it. He should eff off.

[DavidW]

Who said anything about not having it serviced for 20 years? I only said that the boiler was 20 years old.

I only moved into the house last January and the previous owner had it serviced before that, so it is just coming up to it's next service. But have you tried getting a service just before Christmas?

Anyone got any suggestions on how I can check that the pump is always running when it should?

[Chris Hodges]

Had this in our last house, fixed by treating with boiler descaler. However turning the pump up helped enormously, as did removing crud from the F+E tank in the loft (bits of old insulation, sludge etc.) Ours was worse when just the heating was on FWIW.

Chris

[Doctor Drivel]

I'm on about the plantpot, not you.

[Owain]

That's Drivel taking a poke at Mr Plowman. The current dribblebot program is something like

IF input$=(plowman and boiler) THEN output$=(This one never had his boiler serviced for 20 years and boasted about it. He should eff off) ELSE output$=(You are a plantpot)

Owain

[Doctor Drivel]

This man is a Hibernian you know.

[Owain]

Heartless.

Owain

[Jim Alexander]

No this is d-i-y and we'd never be so stupid. Schedule your services before the heating season begins.

[Doctor Drivel]

A heartless Hibernian.

[DavidW]

To be honest I was trying to avoid having it serviced as I was planning to replace the boiler in the spring and did not want to pay for a service and possibly a power flush, particularly as this would have to be done again when the boiler was changed.

I have already checked the pump is free by removing the inspection screw and turning the spindle. I can also hear the pump turning. What I can't check is whether the pump is stopped when it should be running. I can think of two possible reasons for this; a faulty over-run thermostat or a semi-knackered pump.

I would change the pump stat, as it is cheap, if it wasn't for the horror stories I have read about problems when you start opening up the Apollo Fanfare (CO leaks etc)and, according to the installation/service guide on PartsArena, you have to remove the inner cover to get at any of the thermostats. Does any one know a way round this?

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "DavidW" saying something like:

Never mind the rantings of Dangerous Dribble. He's all excited because the 2007 catalogues have hit his desk.

[DavidW]

Thanks for all the suggestions. I have a few more questions.

The photo at

shows the inside of my airing cupboard with the main components marked. The general layout is follows the installation manual for the Apollo Fanfare, i.e. Combined feed/vent pipe and an auto airvent in the primary to the HW Tank. In addition it has an Aerjec Air separator. I can understand why this might be necessary, but dont' undersatand how it can work with a combined feed/vent. Also it has not been installed according to the instructions on the Circulating pumps web site, see

my question are:

1. Is the airjec actually doing anything and if not why not?

1. Could it be the cause of my problem (banging explosions) or contributing to it?

Lastly, here's a suggestion for Dr D:

Speak No Drivel! Hear No Drivel! See No Drivel

[Andy Hall]

To some extent, yes.

If air is entering the Aerjec from the boiler, some will tend to find its way up the combined feed/vent pipe rather than the pump, but as you say, it's not a good arrangement.

The two illustrations on the Circulating Pumps web site are the best orientation, but the one you have would also be OK with three modifications:

- Alter the feed/vent pipe at the loft tank so that it loops up over the tank and makes a vent pipe only.

- Add a feed pipe (15mm is OK) from the bottom of the loft tank to the side of the Aerjec where the pump is now connected

- Connect the pump to the currently blocked off connection.

If you look at part 11334 on

you will see a diagram showing this as a valid option.

However, since you would probably want to turn the device to put the side pipe position next to the wall to make a neater job, it may make more sense to rip the thing out and install it on its side anyway (which is supposed to be a better solution. Personally, I've used both and didn't see a difference though.

Is there a lot of sound of air etc. through the pump? If there isn't, then probably not. However, I would still sort this one out as a matter of having a clean installation.

[Doctor Drivel]

I don't look at your foreign types of catalogues.