Baxi Boiler tripping out

[Slaydeuk]

I have a Baxi Solo HE boiler and yesterday evening, for no apparent reason, the boiler tripped out. Both HW and CH lights on the controller were on, the lockout light on the boiler was on and the ''Mains On'' and ''Boiler On'' lights were both out. I pressed the lockout switch, the power light came on and the the boiler started. It worked OK for the rest of the evening.

This morning the heating did not come on and I found the same situation - lockout on and the green lights both off. Again, I pressed the lockout button and the boiler started. It is still running as I write this.

An additional bit of information: this morning, with the boiler tripped, the pump appeared to be running, but all the pipes in the landing cabinet containing the pump and the Megaflow tank were cold. The boiler is in the garage.

Can anyone suggest what might be the fault. The maker's fault finding charts don't seem to cover this problem.

 

[stem]

A little odd, because the mains light should be lit when the electricity supply is present, you say the 'Mains On' light wasn't lit, suggesting no power was present, yet it must be if the boiler started up when it was reset.

Anyway, as far as I can remember, the lockout light either remains 'on' or 'flashes' which indicate different faults. If it is flashing, the boiler has overheated for some reason, perhaps because there is insufficient water flow through it, or thermostat failure. If it is permanently lit that is 'Ignition Lockout' and means there is a problem with the the boiler such as low gas pressure, or the condensate trap is blocked etc., so for safety it has shut down. So really, you will need to have it examined by someone suitably qualified to test the various components.

 

[Slaydeuk]

Thanks for that. I also am puzzled as to why the mains light was off and yet the lockout light was on permanantly. When I pressed the lockout button the mains light came on straight away and the ''Boiler On'' light followed shortly after. I have been unable to find any information covering the lockout light being on on its own.

I'll have to wait and see if it occurs again and then try to find the reason.

 

[Slaydeuk]

As you were! The boiler has just tripped again and this time it makes more sense. I find it difficult to believe that my memory of the lights last time was completey wrong, but this time the red light was flashing and the power light was on. Rather than embark on the sequence of tests in the overheat lockout check list, I pressed the reset button and the boiler started. Does the fact that it restarted so easily point to any particular fault?

 

[Slaydeuk]

Further update: The boiler has tripped again and probably did so soon after I last restarted it. The situation now is that if I restart the boiler after a trip, it runs for a while and the a banging occurs in the boiler and it trips out. It sounds as if the water in the boiler is starting to boil. If I restart it straight away, the banging recurrs and the boiler trips. I have now switched off the boiler and would welcome some suggestions as to further action. It sounds to me that it could be the temperature thermistor, but I would welcome comments from someone with specialised experience with these boilers.

 

[kidgreen61]

It sounds as though you need to look at your pump!

 

[Slaydeuk]

No. I knew it wasn't the pump, as the pump has been running throughout and it has obviouisly been moving the water judging by the temperature of the adjacent pipes. Cutting a long story short, it was the PCB. I eventually realised that I would have to work through the tests on the 'overheat lockout' page of the servicing instructions, which concluded that it was the PCB. As it happens, I had installed this boiler about six years ago, replacing an identical one (can't remember what the problem was at that time). Happily, I decided to keep the old PCB, which was OK, so I have just now replaced it and the boiler so far is working fine. I just hope it continues to do so.

Thanks to everyone for their interst and help. Fingers crossed.

 

[stem]

"Flashing light (Overheat Lockout)", "banging", "sounds like the water is boiling", would all indicate either insufficient flow, (which is probably why kidgreen61 suggested the pump) or thermostat failure causing overheating. However, as the thermostat works in conjunction with the circuit board, your theory is feasible I suppose, no doubt time will tell.

 

[Slaydeuk]

Fingers crossed didn't work. The boiler tripped again on overheat last night. After a while I was able to restart the boiler, which was still running when it stopped at 10:30 pm on the timer. As I expected, it fired up at 6:30 am on the timer and is still running as I write this (at 8:50). It seems to me that the pump is OK and the PCB is OK, although the series of checks in the manual for an overheat lockout pointed to a duff PCB. I changed this to a spare and the boiler is acting exactly as it did with the original PCB. I am guessing that the fault is in the Flow Temperature thermistor which should stop the boiler from overheating. I have no description of the detailed workings of the boiler temperature controls, but I suppose the boiler is eventually cutting out on the Safety Thermostat as the water temperature in the overall CH system gets up to an unsafe level. Starting from cold, I would expect it to take quite a while to get to this temperature. (still running at9:10).

My plan of action now is to replace the flow temperature thermistor and hope this fixes it. I suppose it could be the fan temperature sensor as this is connected in parallel with the flow temperature thermistor. I welcome any comments or suggestions on my plan.

 

[Dean744PiN5]

First of all stop throwing parts at it hoping that it will fix it, it's most likely a circulation problem, what tests have you actually done to ascertain the pump is ok?

A working but weak pump can start to cause o/heat lockouts as the boiler gets up to temperature but the temperature differential is too great, you would need to measure the flow and return temps to confirm this.

 

[stem]

Has anything else been changed recently? for example have you fitted TRV's to the radiators? Do you have a by-pass pipe with a valve, and if so, has the valve's setting been altered? Have you changed the pump speed? Or anything else that may have effected the flow of water through the boiler.

 

[Slaydeuk]

Thanks for the speedy replies dean and stem - you've caught me in time to stop me rushing out to buy new flow thermistor and safety thermostat. I have judged the pump to be OK as it is definately shifting the water - all the radiaters get up to full temperature as quick as they always have. I have changed nothing recently. The pump has no bypass valve, I have never touched the speed since I moved into the house about 8 years ago. Most of the radiators have TRVs which seem to be doing the job. By the way, the boiler is still running at 10:00 am and the house is comfortably warm. I would have expected it to have tripped out by now or certainly stopped burning. As far as I know, it has been firing continuously since 6:30. I am expecting it to trip out on the safety thermostat, if this is the ultimate temperature cut-out. I'm having a coffee now and will check for further replies before throwing money at the boiler.

 

[Agile]

Water flow through the boiler is totally independent of the internals of the boiler.

But you have not done what most engineers would do without thinking and that is to measure the temperature of the flow and return pipes at the boiler at startup. We usually just do that with our hands as that's accurate enough for this test. Delay the morning start and do that manually.

There should be a difference of about 10-15 degrees providing the water flow is correct.

If the flow is low then the differential will be high and the boiler will tend to overheat.

I don't know what your problem is but expect it to be associated with the pump. If you can overcome your dismissal of the pump as the problem then there are a couple of simple tests you can do. Listening to the pump with a mechanical stethoscope ( screwdriver on pump and ear ) is a simple one. Other is to measure the voltage supplied to it and the current taken.

A simple trick is to reselect the pump speed ( should be on "2" ) as sometimes the switch contacts become high resistance. Sometimes the torque is reduced and the pump does not start reliably usually because of dirt in the pump or the start capacitor losing capacitance. See the FAQ for how to do the finger test.

Tony

 

[Dean744PiN5]

first thing you need to do is measure the flow and return temp, everything else is futile until this is known.

 

[sooey]

Haven't read all the thread, has anyone mentioned checking the f&e cistern?