Baxi WM 512 RS - HELP

I'd check you have sufficient water in the system, as Ian has suggested, before condemning the pump. If need be, drain some off and see if the system refills.

Just to update you and to answer Hugh Jaleak, the CH water (when it’s working) is reaching all rads to the furthest point
I have noticed this evening that each time it shuts down, after 10-15 mins, the pilot light is going out and I have to re light it.
Once it’s re lit, the boiler is firing up again and heating the rads.
Don’t know if that carries any significance

as I said above, based on your knowledge and advice I will try and buy a pump and swap it out
I assume the pump is as old as the system itself so could be the failure point.
If not completely failed, weakened sufficiently to cause these issues

thanks again

Sorry Hugh. Your last post has just come through
I can drain the system down but I’m not sure how to fill it back up.
The boiler is in the loft and it does have a header tank above it which connects to the boiler. Is this how it’s filled?
This would be an automatic top up?
This is where Ian said there could be a blockage?

sorry for the questions. I don’t have the knowledge/experience that you guys have

I thought you said the gas valve solenoid was operating but the burner was failing to come on....

A failing pump etc is easily diagnosed by feeling the temperature across the boiler pipework...with a cast iron heat exchanger it should gradually come up to temp with 10 to 20 degree drop across the pipes.
A red hot flow pipe indicating poor flowrate.

Hi Gas Guru
You are correct. Previously it wasn’t firing up but I managed somehow to get it firing up for 10-15 mins at a time
There is a big difference between the 2 pipes coming from the boiler.
One of them could burn you if you were not careful and the other is luke warm
The pump is also extremely hot
It does make sense what you and others have said about the pump
If it’s not working correctly, not circulating heated water fast enough and the boiler detects that the temperature is too high in the boiler and therefore shuts down.
If I replace the pump it has a fair chance of resolving it but if it doesn’t, at least it’s one component eliminated from the cause
I’m going to try and get one tomorrow

this is an image of the pump which I would assume is fairly standard

Paul309652 said:

I have noticed this evening that each time it shuts down, after 10-15 mins, the pilot light is going out and I have to re light it.

Click to expand...

If the pilot light goes out when the main burner turns off I would suspect the gas valve. I have a boiler of similar age and parentage and the only time I've had the pilot light go out unintentionally was during a violent storm with exceptionally high winds.

Likely with a system of that age, it will be fed from a small feed and expansion cistern in the loft. Drawing some water off should cause it to replenish the system via the cistern, but a common problem in older systems is corrosion. This can cause the small 15mm pipe that feeds the system from the F&E Cistern to block. If this is blocked, then over time slight water loss from the system isn't topped up, causing a lack of water in the system, and therefore circulation problems.

If you have a magnet available, check the pipework around the cylinder, coming down from above. A magnet will not stick to copper, but if it's attracted to the pipework at any point, classic sign of a blockage within. If you are planning to change the pump, then system would need to be drained anyway, (I wouldn't rely on the pump valves!), if cold feed is blocked you'll struggle to refill the system. Some pictures of the motorised valve and surrounding pipework could be beneficial, it is also possible the pump is ok, but there is a blockage elsewhere, which would give the same symptoms. If there is an air separator fitted, these are notorious for bunging up. (Looks like a small tin can with 3 or 4 pipes connected to it.)

Given the massive temperature difference though it does seem the water isn't circulating away from the boiler, I'd expect the flow to be warm, but not so hot as you cannot touch it, at least until the system is up to operating temperature.

However, if the Pilot is repeatedly extinguishing, there may be another issue, unfortunately this isn't something that is suitable for DIY. I'd attempt to solve the circulation issue first and see what happens.

Hi all
Just to update you and thank you all for your contributions
The issue of it constantly shutting down was niggling me and not making sense that the pilot would go out as well and then relight
I took a punt on replacing the thermocouple and it’s back running again perfectly since yesterday midday
I can only assume that the thermocouple was breaking down when it got to a certain temperature
For now it’s running great but I take note of all your suggestions and need to look out for/ investigate other potential failure points like the water supply, circulation, corrosion etc and maybe do some planned maintenance to keep it running.
Thanks for your time and your help
My 80 year old parents are warm again due to your support

many thanks

A service would make sense.

I agree with DP, the boiler would certainly benefit from a service, find someone with experience of these older boilers, and who understands them. Not a difficult job to do properly.

As for the system, a bottle of Sentinel X400 might be well worth a go, this can be left in the system for several weeks, before draining, refilling and flushing a couple of times. It wont remove a solid blockage but may help loosen up any sludge in the low spots of the system. Once that's complete, put in a bottle of X100 Inhibitor to protect the system longer term.

first test you should be doing is when it turns off after 10 mins is checking at gas valve to see if you are still getting 240v at it