Worcester Greenstar 35CDi Combi Boiler - Faulty Overheat Stat

[Cornishsmithy]

Evening All.

Just had an issue this morning, where my central heating is not coming on when required via Nest TStat.

Removed Tstat connection still the same,

HW is working on demand as expected,

When activating Chimney sweep Mode the heating comes on and radiators heat up, when using the mode twice, boiler temp and pressure just keep rising, until pressure shut off happens, dial comes out of red and once in green the CS mode continues for the timed duration.

With overtemp stat linkout out the temp reads a stable temp of 72.

Any more ideas, Plumber just called out stating its directing to the failed overheat stat reading wrong temp due to failure as everything else is working as is.

No Faults showing on the boiler either so not faulting out or needing reset?

Nest system is all linked and connected correctly to boiler,
No issues for 2 years since moving in to the property with the Nest Thermostat system already installed

 

[CountryFan]

Who linked out the safety device? I hope it’s been removed. You mentioned the dial in the red, are you talking about the pressure? Sounds like you need a competent gas safe registered engineer.

 

[DP]

Stop tinkering with the boiler. You are going to damage it doing things you should not

 

[Cornishsmithy]

I didnt, a registered gas engineer did as part of his fault finding,

the engineer stated once hit hits red it shuts down for safety

 

[DP]

When activating Chimney sweep Mode the heating comes on and radiators heat up, when using the mode twice, boiler temp and pressure just keep rising, until pressure shut off happens, dial comes out of red and once in green the CS mode continues for the timed duration.

Chimney sweep is to analyse and if need be set up combustion ratios. It is a timed run or will shut down is upper temperature point is reached. Pressure should not keep rising into 3 bar or red sector. That is a service related defect. The pressure does not shut the boiler down, not for that boiler unless I am making a mistake. Once the burner has been off and pump running, the pressure will decrease- this is physics not a boiler defect

OH sensor. Link it out at your own peril. Appliance is called a boiler. BUT it never boilers water. Risk blowing a gasket or distorting the alloy component/s

Temperature is sourced from a thermistor which changes it value when subjected to temperature. This value is displayed as temperature on the display and also is used to control the burner size thus temperature. OH sensor is there to chop the burner if controlled temperature is exceeded so zilch to do with temperature display other than safely shut the boiler down. If thermistor was defective, boiler would not start

I would focus on nest connection as point of start.

 

[DP]

I didnt, a registered gas engineer did as part of his fault finding,

the engineer stated once hit hits red it shuts down for safety

Ask your guy what he is on. I would like to be on that trip too