Baxi WM50/4

[richardandtracy]

I wonder if someone could help me.
I have a Baxi WM50/4 RS SS based CH system. The boiler has started to ignite when the controller is switched off and the pump is off. Initially I thought it must be a faulty controller, and changed the controller. Unfortunately the same thing happened again.

In the last few years I have had to replace the pump, 3 way valve, tank, controller and most of the wiring. The only original parts of the system are the boiler, pipework, tank thermostat and room thermostat and the thermostat leads. The system worked properly for 3 years since the last work I had to do to it.

At the moment, when the system is working, the hot water comes out excessively hot.

I have the entire system on an electrical isolation switch. The boiler works properly for 18-24 hrs after switching on, then it starts to fire up regularly when the controller is switched off. We then isolate the electrical system (no power to boiler, controller, pump etc), and find 24 hrs later that the boiler over heat switch has activated & the pilot light has switched off. This implies to me that the boiler has fired up even with the power off.

I wonder if anyone could suggest possible faults so I can look at areas that might have failed. Due to the age of the boiler, I am concerned that if any parts in the boiler have failed, then I may not be able to get spares.

Regards,

Richard.

 

[Terrywookfit]

The pump and boiler should run together.
They should be connected to M/v orange wire and cyl stat demand.

 

[muggles]

Think you need to get a boiler engineer in to look at it ASAP - if it really is still firing with the power off that could suggest the gas valve is sticking open which is obviously a major safety issue as it could also stick open when the boiler is not lit, potentially causing gas to escape into your house.

Most major parts are still available for your boiler

 

[muggles]

Think you need to get a boiler engineer in to look at it ASAP - if it really is still firing with the power off that could suggest the gas valve is sticking open which is obviously a major safety issue as it could also stick open when the boiler is not lit, potentially causing gas to escape into your house.

Most major parts are still available for your boiler

 

[richardandtracy]

Terrywookfit:
I know they should run together, and did so quite successfully for the last 3 years.
There is now a spontaneous fault and the boiler runs on its own. Just trying to see if someone has come across a similar problem before so I can narrow down the fault finding. The problem is that the fault doesn't re-appear until 18-24 hrs after turning the system back on.

Andrew:
It's a balanced flue so the gas shouldn't get into the house (and I have never smelt any near the exhaust). Your suggestion that the gas valve is sticking open may well be on the right lines. When operating properly, it does go on & off when it should, and does turn off when the thermostat says so. When not working properly, then it fires up and turns off under the control of the boiler over-heat thermostat. Unfortunately I have no information about what happens when the system is switched off - we have never heard it fire up then, but the pilot light goes out after 24hrs or so & the boiler over-heat re-set needs to be re-set.

Regards,

Richard.

 

[Terrywookfit]

If you have not heard it fire up when turned off........How do you know it actually does ??

 

[ianmcd]

sounds like your gas valve is letting by

 

[AGAS]

does it bang when it first fires up

 

[Hot&Cold]

The boiler has started to ignite when the controller is switched off

Have you checked for voltage at the gas valve whilst its in the above status ?.

The system worked properly for 3 years since the last work I had to do to it.

When was it last serviced ?

Some very good information has already been provided above re gas valve letting by you need to have the boiler checked by a rgi.

Excessive hot water and overheat resetting have been mentioned,consider when the boiler is in an off position if the gas valve lets by that gas will be ignited by the permanent pilot and some gravity hw circulation could occur dumping more heat into the cylinder once it cannot disperse of any more heat the overheat will operate.
The pump over run could be intermittently working to disperse the unwanted heat through the cylinder but it depends on what temperature is in the boiler.

You need a rgi

 

[richardandtracy]

Agas,
The boiler does not bang when it starts up, just the usual 'woomph' that signals the flame front progressing across the burner - the same familiar (and not exactly quiet) sound it has always made.

Terrywookfit,
I don't know for certain it fires up when the system is off as I said in an earlier post, I have no information about what happens when the system is switched off - we have never heard it fire up then, but the pilot light goes out after 24hrs or so & the boiler over-heat re-set needs to be re-set. I have made an inference from the fact the over-heat trip has tripped that the boiler has fired up when no power has been applied, inferring also that the boiler has overheated and tripped the over-heat safety cut-out which also switches off the pilot light.

Regards,

Richard.

 

[richardandtracy]

Old & Bold:
It was last serviced last year, the front was taken off the combustion chamber, vacuumed out, all jets pricked & nozzles cleared, exhaust checked for birds nests. Then the thing was closed up, turned on, a CO detector waved near it and in the exhaust & I was relieved of a dollop of cash. Did feel it was a job I could have done, just don't have the right piece of paper.

However, from what is being said here, it does look as if it's the gas valve is going up the creek and it's not something I'm permitted to touch.
Can design a power station from scratch from the fuel inlet to the last bit of the turbine condenser (being a professional mechanical engineer), predict its efficiency +/- 1%, but I'm not allowed to touch my gas valve. Ho hum. Such is the bureaucratisation of life in the UK these days.

Regards,

Richard.

 

[Hot&Cold]

The boiler has started to ignite when the controller is switched off and the pump is off.

Its either an electrical fault or the gas valve is faulty.Could do an easy test

When your at home and you are aware of it burning gas when no demand exists,switch off the house electric (but do that PDQ as a delay could give false result) and see if it still burning gas.

 

[ianmcd]

To let you understand what I mean by gas valve letting by, when there is no demand for heat, the power to the boiler and pump valves etc stops, if the gas valve is letting by the solenoid does not close properly and a small amount of gas gets through to the burner, as you have a permanent pilot this small amount of gas will be ignited, as the pump is not running this small amount of gas will cause the water in the heat exchanger to become excessive and this will cause the overheat thermostat to interrupt the pilot and switch it off, the gas valves are still available but you need an RGI to test and change it.

 

[Terrywookfit]

Its either an electrical fault or the gas valve is faulty.Could do an easy test

When your at home and you are aware of it burning gas when no demand exists,switch off the house electric (but do that PDQ as a delay could give false result) and see if it still burning gas.

Unplugging the gas valve lead would be far easier !.........And less disruptive to the household.