Immersion Heater Thermostat scorching

[StephenB]

When I removed the cover from the immersion heater in order to adjust the thermostat I found the thermostat had very deep scorch marks and I could see sparks when I switched the power back on. However, both the thermostat and immersion heater still seemed to be functioning properly. I swapped the thermostat with the one from the top (booster) immersion heater that had never been used. When I switched on again there was immediately a smell of melting plastic and brown scorch marks began to appear on the thermostat plastic cover. I swapped them back again because at least the original thermostat had melted all the plastic it was going to melt and didn't smell of scorched plastic any more. Both the immersion heaters are Cotherm model ELE-14-IN-800-FAB and the thermostats are model TSR00014. Has anybody seen this problem before? Is it normal? Any suggestions what to do about it? I don't want to leave these scorched thermostats in place even though they still seem to be working to control the water temperature. Any suggestions welcome.

 

[Octopus]

Get the unit replaced before it packs up and leaves you without hot water. The classic signs of a poor connection

 

[Leesparkykent]

Looks like its not making contact with the spade connector on the element properly.

 

[Pete999]

When I removed the cover from the immersion heater in order to adjust the thermostat I found the thermostat had very deep scorch marks and I could see sparks when I switched the power back on. However, both the thermostat and immersion heater still seemed to be functioning properly. I swapped the thermostat with the one from the top (booster) immersion heater that had never been used. When I switched on again there was immediately a smell of melting plastic and brown scorch marks began to appear on the thermostat plastic cover. I swapped them back again because at least the original thermostat had melted all the plastic it was going to melt and didn't smell of scorched plastic any more. Both the immersion heaters are Cotherm model ELE-14-IN-800-FAB and the thermostats are model TSR00014. Has anybody seen this problem before? Is it normal? Any suggestions what to do about it? I don't want to leave these scorched thermostats in place even though they still seem to be working to control the water temperature. Any suggestions welcome.

Replace the stat, as Murdoch said iffy connections

 

[davesparks]

The damage may have spread to the connection to the element itself

 

[ruston]

And close scrutiny of the supply cable would be prudent too.

 

[telectrix]

as above, but why is there a blue cable into the stat?

 

[StephenB]

Yes, I certainly intend to replace the stat, but the fact that when I replaced it with the stat from the booster, that started scorching as well suggests that the problem is with the element rather than the stats. I don't want to replace the element as that involves draining the water so I need to be sure I've solved the connection problem on that side before fitting a new stat. What's the best way to clean and tighten the connectors on the element? As to the blue cable I assumed that one terminal is connected straight through to one terminal of the element while the other goes through the thermostatic switch. Is this not right? It's true that most of the scorching seems to have started around where the blue cable was connected. Yes, there was some scorching on the cable as well so I cut about three inches off of it when I swapped the two stats. It seemed to be clean above that. Do you think I need to change the entire cable back to the timer switch?

 

[davesparks]

as above, but why is there a blue cable into the stat?

Cotherm stats are double pole, the two spades on the back plug in to the heater itself and you just connect L and N onto the stat unit.

The stats are also ridiculously expensive (around £60)

 

[telectrix]

thaks dave.think i'll stick with the old fashined stats.them you can bridge with a bit of scrap 2.5mm.

 

[davesparks]

thaks dave.think i'll stick with the old fashined stats.them you can bridge with a bit of scrap 2.5mm.

You don't have a choice, if it's got a cotherm immersion heater it has to have a cotherm stat, the normal ones don't fit!

 

[Octopus]

thanks dave. think I'll stick with the old fashioned stats.them you can bridge with a bit of scrap 2.5mm.

and there was me thinking you are a 6 inch nail man!

 

[StephenB]

Looks like its not making contact with the spade connector on the element properly.

You're right, when I replaced the stat with the (never before used) one from the booster, that started scorching as well. This suggests that the problem is with the connection between the element and the stat, and that it's on the element side. I don't want to replace the element as that involves draining the water, so I need to be sure I've solved the connection problem on that side before fitting a new stat. Do you have any suggestions on the best way to clean and tighten the connectors on the element? Thanks, StephenB

 

[Lucien Nunes]

You could try pinching the element socket contact slots shut slightly with needle nose pliers, then slide the stat in and out a couple of times to burnish the surface of the points that actually make contact but I suspect it will continue to burn out. When the contacts overheat, the metal loses its spring temper and will never grip the blade on the stat properly again.

 

[davesparks]

Be careful when you are draining the tank if it is an invented one, it needs to be done correctly otherwise they can implode which is a little bit scary and a big bit dangerous.
I saw one implode when a plumber didn't do it right, I think the whole street heard the bang it made.

 

[Leesparkykent]

You're right, when I replaced the stat with the (never before used) one from the booster, that started scorching as well. This suggests that the problem is with the connection between the element and the stat, and that it's on the element side. I don't want to replace the element as that involves draining the water, so I need to be sure I've solved the connection problem on that side before fitting a new stat. Do you have any suggestions on the best way to clean and tighten the connectors on the element? Thanks, StephenB

Best to get a plumber in to change the immersion if you are not sure. As davesparks pointed out especially if its an unvented cylinder.

 

[StephenB]

You could try pinching the element socket contact slots shut slightly with needle nose pliers, then slide the stat in and out a couple of times to burnish the surface of the points that actually make contact but I suspect it will continue to burn out. When the contacts overheat, the metal loses its spring temper and will never grip the blade on the stat properly again.

Thanks for this. I'm a bit scared of anything to do with plumbing but I decided to check out replacing the whole immersion heater, element and stat. It turns out I can get a complete 14" titanium unit from Screwfix for £28 whereas I've been quoted £61 just for the Cotherm stat from Newey & Eyre. It seems I'd better start trying to improve my plumbing skills.

 

[StephenB]

Be careful when you are draining the tank if it is an invented one, it needs to be done correctly otherwise they can implode which is a little bit scary and a big bit dangerous.
I saw one implode when a plumber didn't do it right, I think the whole street heard the bang it made.

Thanks for this, and your previous comments. Not sure what you mean by an invented tank. Here's a photo of the tank. Is this what you mean? I assume I should open some of the hot taps after shutting off the cold supply and before opening the drain, so the tank can back-fill with air from the hot taps while it's draining. Is there something else I should know? Not sure why the tank appears horizontal in this photo. It's obviously vertical from the position of the inlet/drain, the two immersion heater covers, and the text on the label. Thanks again, StephenB

 

[ruston]

Yes , need the air to be replaced as you draw water off or you will cause a vacuum if it is unvented , and may collapse the tank.
Incidentally. It does say on that label 'to use only manufacturers recommended parts'.
if this is a sealed system I would be very careful , as there are regulations as to who can install these.

 

[Geordie Spark]

and there was me thinking you are a 6 inch nail man!

He was - until he realised scrap 2.5 is cheaper meaning more money for Hobgoblin. :8: