Baxi combi boiler issue

Caliban

Standard Member
Hi

Mother-in-law has a Baxi combi that will no longer heat the radiators, hot water through the taps is fine. It is controlled through a Baxi wireless remote programmer. It seems OK because if I turn up the temperature on that to tropical the boiler fires up and both the 'running' and 'radiator' lights illuminate but only very briefly, less than a minute. I suspected the pump but a plumber visited and had some Grundfoss diagnostic device that told him it was running. He suspects the controller but, as far as I can see, it is working properly and communicating with the boiler.

No error code is displayed.

What else could cause these symptoms?

Many thanks
 
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its_all_Greek

Distinguished Member
have you got a thermostat on the system other than the controller, if the controller takes batteries check they don't need replacing, is the pump part of the boiler, are the pipes blocked.....

Try getting a heating engineer to look at it, just because some one is a plumber doesn't mean they know anything about boilers etc, If the controller is the issue its easily proven by a competent engineer
 

Caliban

Standard Member
No, no other thermostat, The controller is fine in itself, it is measuring the temperature accurately and the display is mirroring what happens on the boiler, i.e. turn up to 30 and the flame symbol appears and the boiler starts. But then the boiler cuts out and the controller still shows a flame icon so the controller has not told it to shut down.
 

noiseboy72

Distinguished Member
3 way valve in boiler sticking? This will prevent the boiler from routing the heated water to the radiators and might be tripping the boiler out if the hot water return temp is too high?
 

Fergal82

Distinguished Member
If the radiator symbol illuminates then that means the boiler is acknowledging the demand for heat (rules out controls at this point)

As mentioned above it’s likely the diverter valve. Boiler only fires for a short time because heat isn’t circulating.

Baxi combis have a couple of different diverter valve configs depending on the model / serial no.

Most of the time they can be serviced (the springs / pins stick) or it may just need a new motor.
 

Caliban

Standard Member
Thanks for those replies. Would you expect to see an error code displayed if this valve has a problem?
 

Caliban

Standard Member
Thanks. The plumber (who is not a heating engineer) reckons that the outlet pipe would not be hot if the diverter valve was stuck but I think it's probably hot due to conduction from the pump which is very hot.
 

Fergal82

Distinguished Member
The baxis usually have a motor which moves a spring loaded pin. These pins stick as for probably 5/6months it’s been sat in the same position (hot water)

Quite easy to prove when in front of the boiler.

If he’s proved the pumps ok, the boilers responding to demand and youre getting no fault codes then it’s looking likely it’s that (for me anyway)
 

noiseboy72

Distinguished Member
we had the same issue with our central heating. The 3 way valve stuck then leaked following firing up the heating. A new valve fixed the issue. Not a DIY fix on combi boilers with integral valves.

If the plumber couldn't locate the issue, find another heating engineer...
 

WozzaB

Well-known Member
Thanks. The plumber (who is not a heating engineer) reckons that the outlet pipe would not be hot if the diverter valve was stuck but I think it's probably hot due to conduction from the pump which is very hot.
You might find that the diverter valve is stuck like the guys here said, but not fully shut, so allowing a tiny bit of flow down the heating side. If you run the hot water, does the heating flow(outlet) pipe warm up at all?
 
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Caliban

Standard Member
So it seems like the motor. although doing something, is not turning the valve properly. The valve can be turned manually. The valve was replaced 7 months ago according the service history scrawled on the casing inside the front cover. Going to try a new motor.
 

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