POTTERTON Precision boiler fires up then shuts down after 10-30seconds

We seem to be the owners of a boiler with a life of its own.

We bought our property that came with this boiler, commissioned in 2015. The previous owner had a complete file with the history of this boiler.
British Gas installed it then came out for repairs several times over the years, almost completely replacing it's parts.
10/2015 - replaced controls (twice in the same month)
05/2016 - replaced faulty mid-position valve motor
08/2018 - replaced heat exchanger and PCB
08/2018 - replaced gas valve and fan

Last year it started misbehaving by making this extremely loud noise, the entire box was vibrating, sometimes for a minute long. At first I was just switching it off from the wall, but then we just got used to it. And then magically it just stopped doing it and worked well for a year.

Then we replaced 3 radiators and completely flushed the system.

Last week it started misbehaving again. As and when the thermostat was instructing it to, it was firing up, then it was switching off after 10 to 30 seconds.
The thermostat shows it to be on and heating, but the boiler is just off... no flame no nothing.
Then randomly when it decides it fires up again and runs for a bit then turns off again... all this time, the water is still being circulated through the system as the pump does not stop. Basically the thermostat works well (one of those BG/hive first gen).

We serviced the boiler with a local engineer, that only did the standard procedures. When I asked him of the issue he suggested we call out someone from Potterton as this was beyond him, as the boiler doesn't show any fault codes.

I also bleed the radiators and I had a look at our magnet filter (don't know what's it called) and the water was completely clean when I drained it a bit.

I called Potterton hoping the boiler might have 7 years warranty as advertised on their page, but apparently BG only offered 2 years for this one, and it's only for a few boilers that they offer 5 years warranty.

To sum it all up:

• we have a clean system
• 5 years old boiler with full service history
• fires up then off while pump still on
• no fault lights

I have recorded the on off cycle, maybe someone with experience can listen to the noises it makes.

https://drive.google.com/file/d/15SDU8-dof66rmcvyxS9ivfWaHb9Xe2yz/view?usp=sharing

Bit more info, we have an unvented system, the boiler is in the kitchen and right above it we have the cylinder in an airing cupboard.

Some pictures of your system will make it easier to see what might be causing the problem.

Can you easily see the flow and return water pipes on the side of the boiler?
When it is running, cautiously feel how hot the flow pipe and return pipe get and report back.

I’m guessing the flow will quickly get very hot while the return pipe will remain cold, in which case there is a circulation problem. In which case there may be a blockage somewhere or a faulty pump.

jackthom said:

Some pictures of your system will make it easier to see what might be causing the problem.

Can you easily see the flow and return water pipes on the side of the boiler?
When it is running, cautiously feel how hot the flow pipe and return pipe get and report back.

I’m guessing the flow will quickly get very hot while the return pipe will remain cold, in which case there is a circulation problem. In which case there may be a blockage somewhere or a faulty pump.

Click to expand...

Yes the flow does get hot, but over a couple cycles the return pipe will get lukewarm as well. Also the pump does not stop, so it keeps circulating the water. So no blockage or faulty pump.

unknovvn said:

We serviced the boiler with a local engineer, that only did the standard procedures. When I asked him of the issue he suggested we call out someone from Potterton as this was beyond him, as the boiler doesn't show any fault codes.

Click to expand...

How did he manage to service it when it was doing that ?

It has moments when it runs for an hour or so. And weirdly just before he came it was working fine. It’s really strange how it behaves to be honest. He even measured emissions and all.
I thought by cleaning it the issue would go away.

You are better off junking the boiler..really.
The heat engine in that model came out around 15 years ago and every boiler model it's appeared in has been a disaster.
There are too many design faults...some which ultimately result in a heat exchanger meltdown.
I can almost guarantee it wasn't serviced fully as it's such a lot of work.
I wouldn't waste any time repairing it.
Whatever you do don't run it with that combustion cover off.

I only took the cover off with everything switched off...

Gasguru said:

You are better off junking the boiler..really.

Click to expand...

It’s not something we can near afford!
Why the heck would they carry on making a boiler that’s proven to be $hit.

Back at the issue at hand. It came on for another hour and I could hear some sort of a squirting bubbling noice.
https://photos.app.goo.gl/Pin1YEANdjGXuVov9

Boiler manufacturers have some of the most hopeless management and they make the most extraordinary decisions, many would have gone bust years ago but contract corruption allows them to survive.
Is this a sealed or open vented system?
Is there sufficient water in the system.

Decide whether to replace the boiler or regularly spend money on it.

Of course it could be a controls issue but...

Gasguru said:

Is this a sealed or open vented system?
Is there sufficient water in the system.

Decide whether to replace the boiler or regularly spend money on it.

Click to expand...

It’s open vented.

I wish it would only be a simple choice... who can afford to dash out about £2.5k for a new boiler?!

Turns out we are covered by our home insurance so we got an engineer sent over.
I don’t think he figured out what’s at fault. So he ordered a new PCB cause the reset button is faulty on it.

Sticking end switch in mid pos/ zone valve would be my bet , nowt to do with boiler

Unlikely to be the pcb....id say its probably flow related. Either the system isnt circulating as well as you think it is and the boiler is going off on temp rise or the boiler believes it isnt flowing well. The flow switches are poor on these. Hard to say without being stood in front of it.

petit_pablo said:

Unlikely to be the pcb....id say its probably flow related.

Click to expand...

+1

Update:
After the PCB was changed, the boiler worked fine for about a week... then the issue returned. This time it wasn’t turning back on unless I was resetting it.
So I called insurance again and they sent another engineer who blamed the flow switch. Then another engineer came out to install the part. He wasn’t very happy as he had to drain the system to fit this...
But great news, as it’s been working fine the past two weeks! ‍‍
It’s still making a bubbling noise and it starts at the boiler. Feels like it’s getting air as the water crosses then boiler? Is that a thing? I keep bleeding the system but doesn’t seem right. I hope it’s not going to cause more problems along the way...

Early days....
That flowswitch design has been around the boiler industry for over 20 years and caused so much trouble wherever it's fitted...the braindead designers of that device didn't
understand that heating system water contains ferrous particles so they placed a nice magnet in the switch mechanism...you can guess the consequence including melted heat exchangers.
What's so hopeless for Potterton (Baxi really) is that they had previously used an off the shelf flowswitch that's bulletproof and almost certainly cheaper.
I'd love to know who came up with that boilers design...it ranks among the industries all time dogs..
The design goes back further than I thought...back to the mid 90s when all the 1st generation condensing boilers were failing.
What's equally crazy is BG and the insurance companies having anything to do with them...I've long since booted anything containing that heat engine off the books...it just isn't profitable.