Baxi Boiler 105e Central Heating Issues

Jon566

We are issues with our central heating system, which may have one or multiple causes, and have been trying to get a plumber to come and diagnose and hopefully fix. Unfortunately it seems most plumbers shy away from diagnosing issues and just want repair jobs, so we've not been able to get anyone to come and look. Perhaps it's just a difficult one to explain over the phone.

Are any plumbers able to advise?

The boiler is a Baxi 105e. It is at least 14 years old, as it has an sticker saying an inhibitor was added in 2002.

The symptoms we have are:

1. The burner comes on, and the temperature indicator lights come on up to 80 degrees. The burner then goes off pretty much straight away and doesn't come on again for a few minutes.
2. The return pipe to the boiler is cold.
3. The radiators furthest from the boiler don't get very warm.
4. The pump is hot to the touch.
5. The last radiator is possibly almost empty - when bleeding there is no air or water. It's warmish.

I've tried having a look online at what these symptoms are and suggestions are a circulation or pump problem. Please can you let me know if you'd agree and how best to approach a plumber to get them to agree to come out?

I have tried adding more water from the filling loop, but not sure if this is actually doing anything. The pressure indicator didn't dramatically change. The filling loop looks to already be connected but it's not obvious.

Any help would be greatly appreciated!

unclebulgaria

I cant be 100% certain as I'm not in front of the boiler, are you getting plenty of hot water? It sounds to me like either the main heat exchanger is blocked, the pump is worn and not actually rotating (quick way to check is to put a screw driver tip onto the pump body and put the handle to your ear, listen for a werring noise not a buzzing, buzzing is bad. there is a little speed selector on the pump so when you're listening to it operate the selector to alter the pump speed you should hear a tonal change if its running correctly), either the flow or return pipe, or both, are blocked possibly at the valves under the boiler or pipework.
You need the services of a competent RGi which you're struggling to get. Its not brain surgery to diagnose so please don't be talked into a new boiler from the off, there are ways of fixing this problem without going down the new boiler route, which by the way, if its a blocked central heating system will not be cured with a new boiler!
As I said I'm not there but if you get a guy who dives straight into "oooooooh its a new boiler mate, sorry!" show him the door!

Le_Kirk

Could be the thermocouple that detects the temperature of the water in the pipes. This is normally clipped to the pipe. Or it could be the excess temperature thermocouple but, if I remember correctly, this is a lockout with a reset required.

Jon566

Thanks for the replies. Hot water works fine, and the boiler burns constantly for as long as tap is running.

Listening to the pump it sounds like a whirring sound, but intermittent, not a constant whir - is this normal? The pump, a Groundfos doesn't appear to have any setting to alter pump speed. Looking at some other Groundhos pumps online, they appear to have a dial on the left side, but this one doesn't, so perhaps doesn't have a speed setting?

unclebulgaria

Jon566 wrote: »

Thanks for the replies. Hot water works fine, and the boiler burns constantly for as long as tap is running.

Listening to the pump it sounds like a whirring sound, but intermittent, not a constant whir - is this normal? The pump, a Groundfos doesn't appear to have any setting to alter pump speed. Looking at some other Groundhos pumps online, they appear to have a dial on the left side, but this one doesn't, so perhaps doesn't have a speed setting?

Ah now we're getting somewhere. So we now know that the main heat exchanger isn't blocked or during the hot water use it would struggle and the plate heat exchanger isn't blocked if the boiler is constant during water usage.
Don't worry about the speed selector its not always fitted and I can't remember what year that model stopped or started having one. You'll know when the pump is jammed it buzzes, it could be a pump a little on the weak side due to age and wear but I'm betting a blocked flow or return pipe. The isolation valves below the boiler have taps on them, inside is a ball arrangement with a hole through it, its possible that you have excessive sludge that's started to build up into deposits that are now slowing the flow of the water to such an extent that its not leaving the boiler fast enough before its too hot and it shuts down until the flow has cooled. It needs draining down and the flow and return valves taking off and checking for blockages and if they're clear I'm afraid your next option is a manual cleaning with central heating cleaner or a powerflush.
As for the thermistors being the culprit I doubt it but if you know an electrician with a Tester or an RGi you can check the resistance of the thermistor and compare it against the manufacturers data.

Jon566

If I have the heating on manual and also run the hot tap until boiler is 80 degrees, after turning the tap off the burner stays on a few minutes and the radiators furthest away from the boiler start to warm up. If I do this a few times the return pipe gets hot. Would this still indicate a blockage? Would running the water for a bit cool down boiler components that are triggering the cut out?

Le_Kirk

unclebulgaria wrote: »

As for the thermistors being the culprit I doubt it but if you know an electrician with a Tester or an RGi you can check the resistance of the thermistor and compare it against the manufacturers data.

Given the new info, I tend to agree it is not the thermistor/thermocouple that is at fault.

unclebulgaria

Jon566 wrote: »

If I have the heating on manual and also run the hot tap until boiler is 80 degrees, after turning the tap off the burner stays on a few minutes and the radiators furthest away from the boiler start to warm up. If I do this a few times the return pipe gets hot. Would this still indicate a blockage? Would running the water for a bit cool down boiler components that are triggering the cut out?

Hmm I'm wondering now if the diverter valve is opening fully in central heating mode. It needs the tender touch of a loving RGI. Its all guess work from here without seeing it as we're relying on your description only.