At a complete loss for this one, theboiler sometimes fails to ingnite on both ch and hw, sometimes it ignites with an audible bang, and sometimes ignites normally. the gas safe ing has been out a couple of times and found that the spark electrode is sparking outside the combustion box! fitted a new electrode, and still the same, fitted a new HT lead and earth, still the same, fitted another new electrode.. still the same, called baxi, no joy. Is it worth another new electrode set or can anyone help with another suggestion please?
baxi133he
- Thread starter et08
- Start date
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This sounds like a very simple problem! If only all boiler problems were that simple!
The first thing to do is to measure the width of the electrode sparking gap!
It sounds as if its far too large.
In the absence of a maker's specification then 4 mm is a good default value. As few people carry feeler gauges then its the thickness of a £1 coin!
Tony
The first thing to do is to measure the width of the electrode sparking gap!
It sounds as if its far too large.
In the absence of a maker's specification then 4 mm is a good default value. As few people carry feeler gauges then its the thickness of a £1 coin!
Tony
thanks chaps, if only it were that simple! the gap is 3mm as per the manual, the gas safe eng who fitted the new burner had the box open, cleaned it all out and fitted a new seal.
The baxi people suggested checking the earth continuity back to the incoming mains, did this with a meter and it was 0 ohms, though it may not be under spark conditions. I might try running some sulementary eart wires, the one which comes with the HT lead seems a bit on teh thin side, though i suppose though the voltage is quite high the current will be low, then again at the instant of the spark is it more or less a dead short?
The baxi people suggested checking the earth continuity back to the incoming mains, did this with a meter and it was 0 ohms, though it may not be under spark conditions. I might try running some sulementary eart wires, the one which comes with the HT lead seems a bit on teh thin side, though i suppose though the voltage is quite high the current will be low, then again at the instant of the spark is it more or less a dead short?
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It sounds very odd to me.
Has the continunity been measured from the tip of the spark electrode back to the EHT transformer?
A 3 mm gap should be where the spark occurs as its so much smaller than the ( greater ? ) place its presumably sparking at outside the combustion chamber.
Did the engineer do the most obvious check of the resistance from EHT transformer to the tip of the electrode? ( That may not be zero as many have a built in RFI supressor, these are sometimes a coil on a ferrite core and sometimes a series resistor of about 10K like car spark plug leads. )
Tony
Has the continunity been measured from the tip of the spark electrode back to the EHT transformer?
A 3 mm gap should be where the spark occurs as its so much smaller than the ( greater ? ) place its presumably sparking at outside the combustion chamber.
Did the engineer do the most obvious check of the resistance from EHT transformer to the tip of the electrode? ( That may not be zero as many have a built in RFI supressor, these are sometimes a coil on a ferrite core and sometimes a series resistor of about 10K like car spark plug leads. )
Tony
ET, While following you will need assistance on a RGI, I would remove the cover, turn the gas off and run the boiler to eyeball spark at the electrode tip.
Earth continuity might not be an issue during sparking. Spark condition/ strength may be an issue though
Earth continuity might not be an issue during sparking. Spark condition/ strength may be an issue though
He started by saying it sometimes sparks to earth outside the combustion chamber.
That would indicate a too wide spark gap but he added it was 3 mm.
To me that indicates a high resistance inside the electrode body. On EHT that equates to a significant spark gap of perhaps 2-4 mm inside the electrode body.
That would have been identified by a resistance measurement as I suggested. But that has not been done and the electrode has apparently been changed. Even so I would be asking for the results of this test! faulty batches of parts are not unknown.
Tony
That would indicate a too wide spark gap but he added it was 3 mm.
To me that indicates a high resistance inside the electrode body. On EHT that equates to a significant spark gap of perhaps 2-4 mm inside the electrode body.
That would have been identified by a resistance measurement as I suggested. But that has not been done and the electrode has apparently been changed. Even so I would be asking for the results of this test! faulty batches of parts are not unknown.
Tony
The expansion vessel is ok, the gas safe eng recharged it in feb when new burner was fitted.
I did the suplementary earth wires as suggested by the guy on the phone at baxi, it seemed to work and i thought i had cracked it, however tonight the wife went for a bath straight after the kids and half way through filling the water went cold. The boiler had locked out and was showing an overheat fault. The airbox lid was pretty hot to the extent that the paper sticker on it was scorched! the glass of the window on the conbustion box cover was deformed with a scorching above the inspection window!
Could it be that this boiler has been running too hot and the heat is causing sufficient expansion of the electrodes to either make the gap too big or short together? Why would it run so hot? could it be air getting in where it shouldnt? but it is a new seal on the box lid in feb when the burner was changed. Could it be getting in arround the window? could the box lid be twisted?
I am getting inclined to haul the thing off the wall and replace it with a Worchester, but ithe baxi is only 5 years old, the potterton it replaced was 20+ years old!
Is it worth spending more money to get the bottom of it or should i cut my losses and scrap it?
I did the suplementary earth wires as suggested by the guy on the phone at baxi, it seemed to work and i thought i had cracked it, however tonight the wife went for a bath straight after the kids and half way through filling the water went cold. The boiler had locked out and was showing an overheat fault. The airbox lid was pretty hot to the extent that the paper sticker on it was scorched! the glass of the window on the conbustion box cover was deformed with a scorching above the inspection window!
Could it be that this boiler has been running too hot and the heat is causing sufficient expansion of the electrodes to either make the gap too big or short together? Why would it run so hot? could it be air getting in where it shouldnt? but it is a new seal on the box lid in feb when the burner was changed. Could it be getting in arround the window? could the box lid be twisted?
I am getting inclined to haul the thing off the wall and replace it with a Worchester, but ithe baxi is only 5 years old, the potterton it replaced was 20+ years old!
Is it worth spending more money to get the bottom of it or should i cut my losses and scrap it?
First thing i would do would be to gas analyse the boiler, look what its running at, this would tell you mixtures, ratio etc. Depending on what the result was make an informed decision what to do next. Been to some where the gas valve was a mile out and running incorrect and possibly dangerous, If you have changed the door seal and the burner the heat is still escaping so their is only the heat exchanger sump to check..
Personally i would take out insurance with baxi, and remember all makes of boilers break down, and that comparing boilers of 20 years ago to those of today is like comparing a cart horse with a car, modes of transport but thats it. sorry all the best i dont think theirs an easy fix ,you could have a couple of faults . Hope this helps.
Personally i would take out insurance with baxi, and remember all makes of boilers break down, and that comparing boilers of 20 years ago to those of today is like comparing a cart horse with a car, modes of transport but thats it. sorry all the best i dont think theirs an easy fix ,you could have a couple of faults . Hope this helps.
Thanks, it does help. I will give the gas safe guy a call today. what is this insurance with baxi you speak of? can i buy it on an old boiler with faults or will they smell a rat is i take out some sort of cover and then call them with a fault?
They will cover you straight away even if the boilers faulty,, no probs, number is or one of the numbers is 0800 032 7232, you will have to check the price etc but it does come down year after year, Then no matter how many parts and time your covered all the time.
Oh what a dilema! called baxi, £289 for fix and year cover. I wish i had known in feb when it got a new burner £200 and last month when it got a new diverter valve £50 !!! Its still cheaper than a new boiler but then again the new bioler would have a 2 year or more waranty. The next year of cover with baxi is FROM £131, which suggests that they might load it up if they have spent a lot in the first year.
Fortuneately the weather is quite warm so i can give it some thought overnight and make a decision tomorrow.
Fortuneately the weather is quite warm so i can give it some thought overnight and make a decision tomorrow.
Please post later when the cause has been identified.
On older cars, a too weak mixture would cause the engine to overheat. We dont normally see anything like that on boilers though.
If the heat exchanger has deposits which prevent the heat removal then that can cause the combustioin chamber to get hotter than normal.
Tony
On older cars, a too weak mixture would cause the engine to overheat. We dont normally see anything like that on boilers though.
If the heat exchanger has deposits which prevent the heat removal then that can cause the combustioin chamber to get hotter than normal.
Tony
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