Vokera Mynute 28e fault - Thermistor/thermostat ?

[MooreCK]

Hopefully someone can offer some advice.

An intermittent fault occurs on my boiler whereby the boiler will not start even though the programmer and thermostats are calling for heat. I have checked all the voltages and they are correct going into the boiler.

When the boiler is turned off and on again the boiler starts. There has been no error code. Spoke to vokea who said it was the main PCB so I changed it but the problem still persists. Called vokera back but they said call an engineer.

Unfortunately I currently cannot afford to do this although I acknowledge this is sound advice.

I am however pretty competent at fixing problems and am not toching the gas side of things so would like to try and fix this myself.

A development today has been that when I went to restart the boiler again there was an error code 2 that pointed to the boiler having overheated. Interestingly I had the night before just turned the heat setting up to max on the boiler. I wonder if this had highlighted the problem.

Could the thermistor of thermostat be the problem here. I assume that both of these could stop the boiler firing if they think the boiler is up to temperature. I guess the pump is not running because it has overun and stopped?

Any advice would be greatfully received.

 

[MooreCK]

An update.

changed the thermistor last week and the problem appears to be fixed, fingers crossed as it has been milder recently and the boiler has not been working as hard.

thanks to vokera technical help who said it was the main PCB and cost me £135. fortunately I figured out that their next guess, change the pump was just that a guess so took my own advice.

 

[StevenJames125]

was this the overheat thermistor that you changed?

 

[MooreCK]

It was the NTC thermistor that goes into the side of the heat exchanger.

 

[StevenJames125]

ah ok - does it have a high resistance reading across the pins?

 

[MooreCK]

I just replaced old for new so did not check the resistance. I still have the old one so will check.

 

[StevenJames125]

ok

did the boiler fire up when turned off and on again but go out again after a short period of time again?

 

[MooreCK]

Turning off and on always started the boiler and it was hard to predict for how long. By the time I spotted it of course it could have been cooling down for quite a while.

What gave me a thought it might be the thermistor was that when i turned the boiler temperature up the problem seemed to occur more often.

As the weather has warmed up it has not had a propper test yet but this is the longest it has run without the fault so far.

 

[MooreCK]

11.9 Kohms but that is when stone cold.

 

[StevenJames125]

I think if it is the fault and it seems to be, the thermistor will usually only be faulty when hot - it may go to infinity reading and cause the boiler to shut down again