Electric Boiler Switch Repeated failures

Aj_newbie

Hello Everyone!!

I have a standard water heater since 2011 in my property.
The primary switch for the heater needs a 13A rating.

Since 2020, the switch is failing repeatedly. 
Happened 3 times from Sept 2020 until today. It warms up, heats up, and then fails.

There has been no electrical changes done to the property, apart from extending one cable by 2 feet in the kitchen in 2018.
The property has been checked and electrical certified in 2019 to be all okay.

Where do I begin to investigate the problem? 
Any advise highly appreciated.

Many Thanks in advance

NSG666

Can you just confirm terminology that you have used?

Standard water heater - do you mean an immersion heater for a tank of water?
Switch - what switch, e.g. spur or thermostat or timer........?
Fails - what exactly do you mean by this?

Photos are always useful.

Cornucopia

Do you mean a timeswitch of some sort, or just a manually operated switch (and if so, is it a standard wall plate or some other type)?

Aj_newbie

NSG666 said:

Can you just confirm terminology that you have used?

Standard water heater - do you mean an immersion heater for a tank of water?
Immersion heater

Switch - what switch, e.g. spur or thermostat or timer........?
A basic spur switch. Photo attached.

Fails - what exactly do you mean by this?

Photos are always useful.

Thanks for your response NSG666. I have answered your questions inline above. And here's the picture. The switch in question is the one with red led on.

NSG666

Ok, by fails I'll take it that it stops powering the immersion and the only solution is to replace the switch and this might be because it is overheating and burning out the connections. 

The above is an assumption and I'm not an electrician but an ex-plumber. I did have a few situations where immersions kept tripping their safety cut-out as they were overheating - replacling them only worked for a short time and I eventully found out that the cable itself had overheated on the connections thereby creating a resistance which in turn generated heat. Replacing the cables (heatproof) between the switch and the immersion always cured the problem in these instances.

It might not work for you but it's an inexpensive thing to try if you can DIY.

fenwick458

this happens. maybe not quite as often as 3 times since 2020 you must have been unlucky or maybe there is another problem like a loose connection at the element or a failing element itself. do you turn it on and off often? what brand of switches are they? who has been replacing these switches, an electrician or is it DIY? when the old switches break, what goes wrong is it one terminal burnt out, the switch goes hard and you can't turn it on or off, or visible cracking on the back of the switch and all the terminals look fine?
would suggest a different brand of switch. or if the back box is deep enough you could try a 32/45A isolator

knightstyle

I had a client who had twosimilar switches fail in 3 years. Found it was dust/dirt getting into the switch contacts and causing hot spots. The switch was below a loft where the son played drums causing the dirt to fall into the switch.  I fitted a surface cooker switch for them and had no more problems.

Ectophile

Get a bigger switch.  When my immersion heater switch started getting hot and smelling of old fish, I replaced it with a 20A one.

Bendy_House

As Ecto says, a 20A switch should handle this with no issues. I presume - hope - it's on its own dedicated circuit with an MCB labelled in your CU 'water heater' or 'immersion' or similar? And that MCB should be 16A rating.

Aj_newbie

fenwick458 said:

this happens. maybe not quite as often as 3 times since 2020 you must have been unlucky or maybe there is another problem like a loose connection at the element or a failing element itself. do you turn it on and off often? what brand of switches are they? who has been replacing these switches, an electrician or is it DIY? when the old switches break, what goes wrong is it one terminal burnt out, the switch goes hard and you can't turn it on or off, or visible cracking on the back of the switch and all the terminals look fine?
would suggest a different brand of switch. or if the back box is deep enough you could try a 32/45A isolator

Thanks.

I have used the brands - Wessex, Click Mode (basically whichever were easily available in nearby shops), with 13A rating.
Someone suggested the brand MK. Is that any good? Or which one should I be going for please?

Aj_newbie

Thank you everyone for the inputs - they are indeed helpful.

The heater switch is in the same room as the heater, so there's a chance of condensation that may be causing this. How do we avoid this?
When I was using the flat, we used to keep the heater room open for ventilation, but not sure if my tenant is doing it at the time.

I plan to go as - 
1. Use a better brand. If mcb is not 16A, will replace that too. Any suggestions on the MCB brand?
2. If 1 doesn't work, will try adding the 32/45A isolator.
3. If 1 & 2 doesn't work, check the wiring and replace.

Fingers crossed