T
TheGasEngineer
Overheating Baxi 100 HE condensing boiler.
First of all switch that boiler off. It's DANGEROUS!! read on...
If you have met a Baxi 100 HE with a melted combustion chamber it’s caused by perished glue allowing the burner ceramic to lift and cause furnace-like volumes of gas/air mixture to enter the combustion chamber.
The ceramic face only becomes loose when it gets hot. When it does become loose it lifts and the fan responds by pumping a vastly greater volume of gas/air mixture into the combustion chamber. For the boiler I have just been investigating the working pressure dropped 3mb which indicates the increase in gas rate. I couldn’t measure the gas rate at the meter because it had overheated well before I could get there.
What seems to happen is the glue begins to fail and little by little the ceramic lifts - maybe over several weeks. So the boiler starts to run hot and I guess this contributes to the failure of the manifold O-ring and maybe even the flow switch. If you think about it, if there is overheating, it must be excess gas. It can't be anything else. The problem is that once the boiler shuts down the ceramic drops back onto its seat, the glue solidifies and amazingly it looks to all intents and purposes like a perfectly serviceable component.
The boiler overheats enough to melt and distort all the lower parts of combustion chamber aluminum and wreck the door seals - it cinders them. Then it overheats and shuts down usually via the fan stat. On stopping, the ceramic then drops back into the metal burner base. When it’s cool enough to handle the ceramic it's held rigidly in place again, sitting there all innocently.
About a year ago I was called to a 100HE and the sump of the combustion chamber and 2 to 3 inches of the lower side walls had melted. It was a mess. I couldn’t think how sufficient gas had entered the combustion chamber to get so hot. Of course the ceramic element was sitting there looking secure in the pressed steel base.
A 100HE kept me baffled for a week. The flow switch had failed and the lower manifold was leaking just to add to the confusion. When to door came off the seals had gone but not cindered. I fitted new ones and left it running. This time it seriously overheated and melted the sump base. I thought I had not put the seals on properly causing the overheat. I talked to Baxi technical but they hadn't a clue. With a new base, flow switch and manifold O-ring in place the boiler overheated again (Arrrrgh!!). It quickly became red hot inside and it roared noisily. I didn't know what the roar was. There was some damage but not too much and so I ran it up again and watched very carefully. Initially the flame looked as it always had from cold - blue and fairly quiet (almost normal). And then bit-by-bit it started to roar and the internals of the combustion chamber turned cherry red. Then in an instant as it was really overheating I happened to see the ceramic lift. I couldn’t believe it at first but then it stuck half out and when it cooled down there it was, jammed solid but at an angle and finally revealing the problem.
I find it shocking that Baxi haven't recognised this fault. From what I see there are multitudes of these boiler breaking down like this and they could be salvaged just by replacing the burner every three years. It just needs Baxi to admit it and put out a general warning. I think a warning is necessary because it's a fire-bomb waiting to happen.
I rang Baxi tech support and really pressed them about the excess heat and they didn't have a clue. There was not one suggestion or offer of help or any interest at all. I told him about the low working pressure and he said this would seriously affect the performance of the gas valve. Rubbish!! Actually this is where the zero governor is a pain - as soon as the flow restriction of the ceramic was lowered (when the ceramic lifted off its seat) the flow rate through the fan rose exponentially and the valve just increased the flow of gas to match resulting in an inferno in the combustion chamber. If that is not a design fault then I don't know what is...
So if you service the Baxi 100 HE range (or any boiler that uses that burner) I suggest it's replace every third service.
First of all switch that boiler off. It's DANGEROUS!! read on...
If you have met a Baxi 100 HE with a melted combustion chamber it’s caused by perished glue allowing the burner ceramic to lift and cause furnace-like volumes of gas/air mixture to enter the combustion chamber.
The ceramic face only becomes loose when it gets hot. When it does become loose it lifts and the fan responds by pumping a vastly greater volume of gas/air mixture into the combustion chamber. For the boiler I have just been investigating the working pressure dropped 3mb which indicates the increase in gas rate. I couldn’t measure the gas rate at the meter because it had overheated well before I could get there.
What seems to happen is the glue begins to fail and little by little the ceramic lifts - maybe over several weeks. So the boiler starts to run hot and I guess this contributes to the failure of the manifold O-ring and maybe even the flow switch. If you think about it, if there is overheating, it must be excess gas. It can't be anything else. The problem is that once the boiler shuts down the ceramic drops back onto its seat, the glue solidifies and amazingly it looks to all intents and purposes like a perfectly serviceable component.
The boiler overheats enough to melt and distort all the lower parts of combustion chamber aluminum and wreck the door seals - it cinders them. Then it overheats and shuts down usually via the fan stat. On stopping, the ceramic then drops back into the metal burner base. When it’s cool enough to handle the ceramic it's held rigidly in place again, sitting there all innocently.
About a year ago I was called to a 100HE and the sump of the combustion chamber and 2 to 3 inches of the lower side walls had melted. It was a mess. I couldn’t think how sufficient gas had entered the combustion chamber to get so hot. Of course the ceramic element was sitting there looking secure in the pressed steel base.
A 100HE kept me baffled for a week. The flow switch had failed and the lower manifold was leaking just to add to the confusion. When to door came off the seals had gone but not cindered. I fitted new ones and left it running. This time it seriously overheated and melted the sump base. I thought I had not put the seals on properly causing the overheat. I talked to Baxi technical but they hadn't a clue. With a new base, flow switch and manifold O-ring in place the boiler overheated again (Arrrrgh!!). It quickly became red hot inside and it roared noisily. I didn't know what the roar was. There was some damage but not too much and so I ran it up again and watched very carefully. Initially the flame looked as it always had from cold - blue and fairly quiet (almost normal). And then bit-by-bit it started to roar and the internals of the combustion chamber turned cherry red. Then in an instant as it was really overheating I happened to see the ceramic lift. I couldn’t believe it at first but then it stuck half out and when it cooled down there it was, jammed solid but at an angle and finally revealing the problem.
I find it shocking that Baxi haven't recognised this fault. From what I see there are multitudes of these boiler breaking down like this and they could be salvaged just by replacing the burner every three years. It just needs Baxi to admit it and put out a general warning. I think a warning is necessary because it's a fire-bomb waiting to happen.
I rang Baxi tech support and really pressed them about the excess heat and they didn't have a clue. There was not one suggestion or offer of help or any interest at all. I told him about the low working pressure and he said this would seriously affect the performance of the gas valve. Rubbish!! Actually this is where the zero governor is a pain - as soon as the flow restriction of the ceramic was lowered (when the ceramic lifted off its seat) the flow rate through the fan rose exponentially and the valve just increased the flow of gas to match resulting in an inferno in the combustion chamber. If that is not a design fault then I don't know what is...
So if you service the Baxi 100 HE range (or any boiler that uses that burner) I suggest it's replace every third service.
