Immersion heater gets hot then thermostat trips, continually.

[The Bedwetter]

We are having some real problems with an immersion heater, the thermostat of which is continually tripping. The vented direct HW cylinder (112litre) is in the loft of a friend’s flat. The IH is a 27" Incoloy running diagonally with a 14" stat and has been installed about for about four months. It failed the other day following a fair bit of use from mate & friends returning from a holiday after not having been used for about a month.

I checked the resistance of the IH to be 20Ω and replaced the tripped thermostat (which had been set to about 60°c), reconnected and everything got hot nicely. The following day: same result. This time I removed the IH and shining a light into the cylinder was surprised to see two stems of a broken element poking upwards and presumably making contact with and shorting the live element – wonderful :dead:. Following the removal of the element remnants I refitted the element as it looked to be in good order (minimal scale) this time setting the thermostat to 55°c. I genuinely thought that this was the problem resolved and had no expectation of the stat tripping again. Yet, this is exactly what has happened.

Any ideas what could be the problem, here? Thanks in advance for any advice.

Note: It is the stat that has tripped continually. The mcb light at the consumer unit remains on.

 

[PETE 123]

I had one once where the element had moved closer to the tube that the thermostat is located in. Best change the lot or take out and check how close they are

 

[Best]

Are you sure the immersion heater cover isn't covered over by something, like cylinder jacket or clothes etc? Puts the cut out off if it is covered.
Unless you are unlucky to have faulty stats.

 

[The Bedwetter]

I had one once where the element had moved closer to the tube that the thermostat is located in. Best change the lot or take out and check how close they are

Interesting. The tube, though, is housed in the sheath - would this be likely to expand? Regardless I think I'll take your advice and replace the element and stat. Thanks, Pete. :wink5:

 

[The Bedwetter]

Are you sure the immersion heater cover isn't covered over by something, like cylinder jacket or clothes etc? Puts the cut out off if it is covered.
Unless you are unlucky to have faulty stats.

No. The cover has had quite a lot of its surrounding insulation foam removed to make access for previous element installations. The cylinder is located in an attic so there is no option to heat clothes.

 

[The Bedwetter]

Thanks for your help, chaps. Would you be able to recommend a reliable 14" thermostat manufacturer as I think it might be worth changing from the type that we currently have.

Cheers.

TB

 

[WHPES]

Sunvic

 

[The Bedwetter]

I will return to problematic immersion heater tomorrow with Sunvic thermostat in hand (thanks, WHPES).


Just one further point. Whilst the replacement IH was getting warm I did notice that the isolating DP switch also becomes pretty warm. I suppose with 12 or 13 amps passing through the cable this might be expected but perhaps somebody could confirm if this is the case? Also when switching off at this isolator there is a little flash visible. I switched of supply at the consumer unit and opened the switch up and the connections look tight. I would expect that if there were to be a problem with the switch then the MCB would trip but this does not happen it's the stat that trips and the water is not anywhere near to hot.

Thanks again for any comments.
:wink5: