Potterton Netaheat 16-22 MkII Overheat Thermo replacement

[speedysteve]

The overheat thermostat is starting to make a lot of radio interference on switch off.
I was pondering how to remove the probe. Sorted. It just pulls out and the new probe pushes in.

 

[speedysteve]

Just an update and info for the archive for others should they search for thermo problems.

The Overheat Thermo for this model is Ranco 404449. T90deg C

Once the new overheat thermostat was installed the water temp only got up to 53 deg C before it tripped out. This was with it set at max! This should be 90 deg C - Hence the T90 deg C!
I put the old thermo back in and all was restored - both the radio intereferance and the water temp at 80 deg C with the adjuster knob set at 3.5 - I have an infrared heat gun measurer BTW...

I called the Potterton/Baxi support line and talked to 2 tech engineers.
Their number is 0870 6000454 - ask for tech support.
Both considered that from the description the new thermo was duff.
I asked them how the thermos were set / callibrated - the answer was, callibrated at factory, they didn't think there was any adjustment other than the main one (knob on the front).
So on to the supplier of the new thermo to get another one sent out.

I looked at the new thermo very carefully and discovered that there is indeed a potentiometer adjustment accessible through a tiny hole on the side of the unit and with even smaller arrow indicating + / -.
Tests in cups of hot water proved that the thing was set completely wrongly.
After increasing in the + direction and refitting the water temp was up to 80 deg C (as it should be) and this was attained with the main adjuster knob at the same settling as the original thermostat.

So I will soon have a spare thermostat.

In general, the condition of this 20 year old boiler is pretty good.
I replaced a faulty relay unit a couple of years ago.
All seals are in good nick and the case fits very well.
I always have a CO monitor next to the boiler to warn of leaks and would reccomend this.