Electric Boiler Switch Repeated failures

Bendy_House

You need a 20A rated switch. Higher is fine, tho' terminal holes will be that much - and unnecessarily - larger. If you find a 13A version, don't touch it!

No, this has nothing to do with condensation. It's either that the switch you've used is really only designed for 13A (too low, as it'll be constantly running on max), or that the cables wire ends are dirty or corroded so are not making a good electrical contact with the switch's terminals. (Or possibly an under-rated CABLE has been used to supply this, in which the WHOLE cable will be getting very warm! But I doubt it's this.)

So, when you remove the old switch, check the condition of the bare wires, and clean them up by scraping them if needed.

MCB make, whatever the rest are. Just 16A, tho'.

Aj_newbie

Hello everyone!

Here are the updates (and some findings)
1. The previous switch was 20A (which failed around 5 weeks ago) (Previous to this one, were 13A)
2. I have now fixed a 13A fused switch. The switch is turned on 2 times a day - for 5 hour each.
3. The switch warms up a bit. The fuse area is warmer than other parts of the switch obviously.
4. The wire going out from the switch to the heater is warm. The wire coming into the switch from the mains is normal.
5. I have kept the thermostat settings to 3 (out of 5). It was 5 before.
6. No improvement regarding 3 &4, after thermostat change.

What might be wrong?
Mine is Santon Premier Plus heater. Electric. Is it time to call their customer service?

Bendy_House

Aj_newbie said:

Hello everyone!

Here are the updates (and some findings)
1. The previous switch was 20A (which failed around 5 weeks ago) (Previous to this one, were 13A)
2. I have now fixed a 13A fused switch. The switch is turned on 2 times a day - for 5 hour each.
3. The switch warms up a bit. The fuse area is warmer than other parts of the switch obviously.
4. The wire going out from the switch to the heater is warm. The wire coming into the switch from the mains is normal.
5. I have kept the thermostat settings to 3 (out of 5). It was 5 before.
6. No improvement regarding 3 &4, after thermostat change.

What might be wrong?
Mine is Santon Premier Plus heater. Electric. Is it time to call their customer service?

What's wrong? The bits in bold, I guess!

Why on earth would you fit a switch that's running on virtually its max rated capacity? Esp when 20A versions are more common?

But the real warning sign here is the warm cable to the immersion - that would suggest it's seriously underrated. It should also be heat-resistant cable - is it? Look along the outer insulation - and printed info on there? Can you measure the diameter of the whole cable (not necessarily useful, but it could be an indication of actual wire size).

I suspect that the issues may have been caused by the actual outlet wire overheating where it's compressed by the screw terminal in the FSU - the whole cable already seems to be running on 'max', so anything that reduces its size even marginally could cause a heat spot and damage to the switch.

Close-up photos of the cable, please?

Ectophile

Use a better brand. If mcb is not 16A, will replace that too. Any suggestions on the MCB brand?

The MCB should be the same brand as the manufacturer of the consumer unit.  Consumer units don't all have exactly the same fittings, and no manufacturer will warrant that their unit is safe when using any other manufacturer's MCBs.

The MCB should be sized to protect the cable.  A 16A one should be fine for a 13A load.  You haven't said what's there at the moment.  A 20A one could be OK if the wiring can take that, but not if it can't.

fenwick458

switching it on and off under load is probably why it's failing. how about a 16A timer, set it to your desired on/off times and leave the switch alone?
https://www.google.com/search?q=16A+immersion+heater+timer&rlz=1C1VDKB_en-GBGB940GB940&oq=16A+immersion+heater+timer&aqs=chrome..69i57j0i390l3.4712j0j7&sourceid=chrome&ie=UTF-8

Bendy_House

Is no-one concerned that the cable coming from the FSU to the immersion heater becomes warm in use?

Ectophile

Bendy_House said:

Is no-one concerned that the cable coming from the FSU to the immersion heater becomes warm in use?

It depends on how warm "warm" is.  Ordinary PVC cable is designed to last for years with the copper inside reaching 70°C.  Heat resistant cables may go up to 90°C or more.

Bendy_House

Ectophile said:

Bendy_House said:

Is no-one concerned that the cable coming from the FSU to the immersion heater becomes warm in use?

It depends on how warm "warm" is.  Ordinary PVC cable is designed to last for years with the copper inside reaching 70°C.  Heat resistant cables may go up to 90°C or more.

Argh! Surely not from the inside, tho'?! I've no idea - just how 'warm' can cables become before being a concern that they may be under-sized?