Expected Ohms reading Baxi Overheat Stat

[Lostdotfish]

My old Baxi 105e keeps going into overheat cutoff mode and I am fairly sure the Overheat Stat is to blame...

Can someone confirm what the expected Ohms reading is for the 7671968 part please?

Baxi Potterton Overheat Thermostat 7671968

The Baxi Potterton overheat thermostat is compatible with Precision, Promax SL, Solo HE and HE A, Promax, Main HE A, Solo IE, Gold, Solo IE ErP, Gold ErP, Main Heat ErP, Combi (Condensing), 80 He, Promax SL ErP, Platinum, 100 He, Ecogen, 50 He, and Barcelona units. The thermostat allows the user...

www.cityplumbing.co.uk

I am getting a very low reading of less that 1 ohm at room temp...

 

[Harry Bloomfield]

I am getting a very low reading of less that 1 ohm at room temp...

That is correct...

A 'dead short'/ less than 1 Ohm, at below the trip temperature, and it should open / high resistance, above the trip temperature.

 

[Lostdotfish]

That is correct...

A 'dead short'/ less than 1 Ohm, at below the trip temperature, and it should open / high resistance, above the trip temperature.

So the overheat stat is ok and the problem is elsewhere?

 

[Lostdotfish]

Ok so moving on to the DHT thermistor

3k ohms and some change

and the same for the one above the Overheat Stat

Are they both in spec? Seems a little low to me - measured in circuit

Edit - system may still be quite warm so I'll measure them again in an hour or 2... I guess if they are both reading around the same - then they are both probably fine...

 

[Harry Bloomfield]

So the overheat stat is ok and the problem is elsewhere?

I didn't say that. The stat should be closed at room temperature, but open, at the temperature it is designed to open. You have checked the first, but not checked the latter - though likely it will be fine. The best way to be sure, is measure the temperature of the boiler, when it opens.

 

[Harry Bloomfield]

and the same for the one above the Overheat Stat

Are they both in spec? Seems a little low to me - measured in circuit

There is a wide range of thermistors, each with different temperature versus resistance, so without knowing which thermistor, it is impossible to say whether it is in spec. or not..

As this is a room sealed gas appliance, and you would seem not to be gas qualified, I don't think you should be messing about in there at all....

Rather, it might be more sensible of you to assume the boiler is simply over-heating, if that's what the diagnostics suggest, and look for external to the boiler causes..

 

[Lostdotfish]

I didn't say that. The stat should be closed at room temperature, but open, at the temperature it is designed to open. You have checked the first, but not checked the latter - though likely it will be fine. The best way to be sure, is measure the temperature of the boiler, when it opens.

tested the overheat stat by heating it up with a controlled heat source and it clicks and goes open - so fairly sure that is working as intended.

I'm fairly sure the other 2 thermistors are fine too - so guessing the problem lies elsewhere...

We had the main diverter valve and pump changed last year and the system was ok through that winter - boiler is very very old now - so probably at the point of not wanting to throw any more money at it - just wanted to make sure it's nothing simple before getting replacement quotes...

 

[gas112]

what neon is on/flashing when it fails