Immersion heater stat keeps tripping

[Dunx]

Hi All,

Called by plumber to troublesome IH which keeps tripping, he has changed the immersion heater and the stat already so its no a dodgy stat. Oddly the tank is one of these rectangualr ones similar to Elsan but it has no makers name on. The immersion heater is vertical but fitted from underneath.

I can't figure anyreason why the stat would repeatedly trip the over temp button....Any ideas?

Ta

 

[Andy™]

whats tripping

 

[Dunx]

The new type immersion heater stats have a button that pops out at 65 degs approx and disconnects supply.

 

[Andy™]

faulty stat not turning off, so over temp stat is tripping?

 

[ProDave]

I think it's more like 90 degrees the safety cut out pops.

Make sure the normal stat. is set well below that, no more than 70.

I must admit I had one like this. It too had had 3 new stats fitted by a plumber (the previous 2 were still left next to the tank, all identical)

I got it working by setting the stat. to it's minimum setting which I think was 30 degrees, and the water was still pretty dam hot, but it didn't trip any more.

I concluded a batch of dud thermostats calibrated wrong. I never did try a different one sourced from a different place.

 

[NozSpark]

I've just had a top entry one do this,,, I replaced the stat from an old (degF) one that didn't have over temp to one that did...

ended up changing the stat (again).... they haven't phoned me so it ust be OK

 

[Dunx]

Yup, I guess I will try another stat and set it low. I think the new ones only have a small range tho? Maybe with a max of 60deg... I wondered whether it could be anything to do with the upside down position but couldn't think of any logical reason for that!

 

[ProDave]

When you say upside down, are you saying the immersion heater screws in from the bottom of the tank, rather than the side or top? Never seen that.

If the tank is sludged up with scale or crud, then a heater mounted like that, the thermostat pocket might be covered in sludge, so not seeing the true water temperature, which in any case will be lower at the bottom of the tank.

 

[NozSpark]

If the element comes from below then I'd fit the shortest state that you can get

 

[chrishaworth]

Had one a while back which turned out to be a fire back boiler in parallel with the heating coil. The fire took the tank temperature past the stat tripping temp but they only noticed when the water had cooled and the fire was off so it showed up as a weirdly intermittent fault.

Cheers. Chris