Combi boiler fault

[stevo72]

Hi

I have a fault with a Baxi HE 133 combination boiler. I had a gas boiler engineer round to inspect it. He suggests that the boiler requires a new PCB electronic board. But I would like a second opinion, or as many informed opinions as I can get before forking out £200+ to have this done. I'll try and give as many details on the symptoms I can.

There are two symptoms:
1. After 10-20 minutes of operation the boiler shuts down and the indicator lights tell me that the boiler is "overheating". This is the light panel combination as according to the boiler manual. The engineer went through the checks in the manual for this fault and they were ok.
2. The water pressure is regularly dropping both when the boiler is fired up and when the boiler is idle e.g. during the night.

However, these issues are intermittent. If I close off most of the thermostats on the radiators and just leave 3 rads on then the boiler will operate perfectly well for up to 6 hours providing hot rads and does not appear to lose water pressure. I then open up more radiators and the verheating/drop in water pressure problems re-occur eventually.

I get the impression one of two things are happening:
1. Either the PCB and sensors are correct and the boiler really is over heating in which case insufficient water is entering the heat exchanger. Which could be a sticky or clogged valve?
2. Or the PCB and sensors are faulty and the boiler is not overheating and the electronics are giving a false reading. But if this is the case why is the water pressure dropping?

This is a link to the boiler manual
http://www.gasapplianceguide.co.uk/Baxi_HE_Plus_Range.pdf

Any advice welcome and a very merry Xmas to all😀

 

[Blake]

i would check the combustion door seal first as it's a common fault on these. They get brittle and allow heat to escape which trips the overheat stat.

The pressure drop could be a leak somewhere on the system, a faulty expansion vessel or a faulty pressure relief valve. I would not think the two faults were connected.

Also check the burner as they have a gauze on them that is also prone to getting brittle and falling apart.

 

[stevo72]

Hi bronzino

Yes when the boielr was first installed the combustion door seal was replaced 3 times apparently because they were not using the right seal for the boiler. That was 4 years ago. If the seal is failing again do you think it would exhibit any visible symptoms such as steam coming out of the flu?

All my rads and pipework are above the concerte floor and show no signs leakage. The PRV is also a possibility and I will try and keep an eye out for water being released out of the overflow pipe but so far have seen none.

The boiler is currently operating fine with just 4 rads open. If I open up more I expect the symptoms to re-appear. Perhaps this could be because more rads open requires a higher water pressure in the exchanger triggering the fault?

 

[Blake]

It would not show any visible signs, just trips the overheat stat from memory. A new seal pack is only about £20 I think.

You obv have a circulation/overheat issue which is probably linked. The door seal would still be my first check, I would not suspect a faulty PCB myself but I could be wrong.

Has your gas engineer not called the baxi tech line whilst on site? They will get him to check and test parts plus they know the common problems with each boiler model.

 

[RoryD]

i would check the combustion door seal first as it's a common fault on these. They get brittle and allow heat to escape which trips the overheat stat.

The pressure drop could be a leak somewhere on the system, a faulty expansion vessel or a faulty pressure relief valve. I would not think the two faults were connected.

Also check the burner as they have a gauze on them that is also prone to getting brittle and falling apart.

That's the call I'd make bronzio. I've had a couple in recent weeks where there have been cracks in the burner and this in turn is directing the flame onto the door seal. Obviously the fan overheat stat operates. Solution is new burner and seals. Give away can be white powder in the boiler.

 

[SPC]

Just to bring up an old thread; did you get the boiler sorted stevo?? And if the overheat was too trip on this boiler, once cooled down would it fire back up? Or is it a manual resetting one?

 

[stevo72]

Hi SPC

No I haven't taken any action yet. I can get the boiler to work to a limited capacity and one week it worked for 5 days without trouble but on reduced radiators. To get it working again after over-heating failure, I close off all of the rads apart from one and the bath towel rail, and let it run until turns off the burner as it should do when the sufficient hot water has been supplied. At this point I can hear a valve clicking over. Then I open up a couple of more rads and it works fine for the rest of the evening.

I'm unsure at the moment whether to have the problem fixed or replace the boiler with another make. My property is up for sale and a new boiler with a new warranty would be a good selling point. But on the other hand I think the chaps above are right and it may just be a failing combustion box seal (again).