My immersion heater plugs into a socket in the airing cupboard. I know that this is wrong but it has been like that since we moved in 30+ years ago. We rarely if ever use it - maybe twice a year. I would like to have this on a timer for a few weeks while the CH system is being serviced/repaired (new rads etc.). Is it ever safe and OK to plug in a timer and then an immersion into that? Most I have seen are rated at 13A but then say not to use with immersion heaters!
Immersion on plug-in timer?
- Thread starter Vicario
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BS1363 13A sockets are rated for 13A loads but only for intermittent use. Not for loads which are likely to be on for hours at a time.
A plug in timer makes this worse, as there are more connections and parts to overheat.
Removing the timer and just plugging into the socket would certainly be better.
Cost of operation isn't likely to be much different, as the immersion heater contains a thermostat which will switch off when the water is heated.
A plug in timer makes this worse, as there are more connections and parts to overheat.
Removing the timer and just plugging into the socket would certainly be better.
Cost of operation isn't likely to be much different, as the immersion heater contains a thermostat which will switch off when the water is heated.
It depends. I have known such an arrangement that has been fine 'forever'.
The timer might be 16A so irrelevant.
The timer might be 16A so irrelevant.
there are a vast number of hardwired timers on the market, designed for immersion heaters and rated at 16A.
these days most are electronic programmable, but you can still get ones with a rotating dial which are totally easy to understand and operate.
useful link
these days most are electronic programmable, but you can still get ones with a rotating dial which are totally easy to understand and operate.
useful link
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Main problem is the 13 amp fuse, for a fuse to rupture it needs the melt the wire inside the cartridge, so must produce heat, so any 13 amp socket should be in free air to remove the heat, a 15 amp socket does not have a fuse, so runs far cooler, as does a 16 amp socket like used in many other countries of the world.
But because the fuse is only in the live, neutral must not be fused, in the UK getting line and neutral the right way around is important, so you can use French plugs and sockets, but not German, and even the French have moved to the German Schuko socket, so getting a plug and socket which is non reversible is a problem, we could get the German sockets easy enough with timers etc, but in an airing cupboard is hardly free air, so British 13 amp is not really an option.
The immersion heater takes hours to heat 40 gallons at 15ºC to 65ºC with 3 kW will take 3h 32min, but normally the thermostat will switch on at 55ºC and off at 65ºC so down to 43min, which means it does not heat up the plug so much, calculator here so as long as not switched off, the time the heater is on is much reduced. Only when running a bath will one be looking at hours, as long as water not allowed to cool.
The reverse is true, to cool 40 gallons of water will take time, quite a long time, my boiler switches on 4 times a week for ½ hour, well only actually runs for 20min which is enough to have hot water in the taps to wash hands, so since it takes so long to cool, having it on a timer if there is a thermostat seems pointless, only reason I have it set for ½ hour is I have no tank thermostat connected to the central heating, so it would be cycling on/off all the time keeping the pipes warm.
You could of course use the timer to limit the one time, say 15min on and 45min off, but that seems pointless.
But because the fuse is only in the live, neutral must not be fused, in the UK getting line and neutral the right way around is important, so you can use French plugs and sockets, but not German, and even the French have moved to the German Schuko socket, so getting a plug and socket which is non reversible is a problem, we could get the German sockets easy enough with timers etc, but in an airing cupboard is hardly free air, so British 13 amp is not really an option.
The immersion heater takes hours to heat 40 gallons at 15ºC to 65ºC with 3 kW will take 3h 32min, but normally the thermostat will switch on at 55ºC and off at 65ºC so down to 43min, which means it does not heat up the plug so much, calculator here so as long as not switched off, the time the heater is on is much reduced. Only when running a bath will one be looking at hours, as long as water not allowed to cool.
The reverse is true, to cool 40 gallons of water will take time, quite a long time, my boiler switches on 4 times a week for ½ hour, well only actually runs for 20min which is enough to have hot water in the taps to wash hands, so since it takes so long to cool, having it on a timer if there is a thermostat seems pointless, only reason I have it set for ½ hour is I have no tank thermostat connected to the central heating, so it would be cycling on/off all the time keeping the pipes warm.
You could of course use the timer to limit the one time, say 15min on and 45min off, but that seems pointless.
what colour is your hot-water cylinder? (this indicates the grade of insulation it has)
are the hot pipes coming out of it, especially the top one, well insulated?
if the cylinder is well insulated, losses are so small that it is hardly worthwhile using a timer, unless you have cheap electricity at certain times (e.g. an "economy 7" type tariff, or PV solar panels.) in which case use as much as possible at cheap times.
A timer will probably cost you around £20 and I doubt it will save you £20 of electricity in the next ten years.
Where did you get this gem from? Being in France recently I saw no evidence of such a change.
Plug in timers on immersion heaters aren't a brilliant scheme- I've cooked 2 over the years (both on exactly the same 'short term standin' sketch).
You can get 20A relays (with 240v coil) quite cheap from CPC or Amazon- your temp bodge can be to connect the relay coil to your existing dhw controller and power the heater from the 20A contacts (use an FCU if you want or use adequate sized cable and an unfused connection unit)
You can get 20A relays (with 240v coil) quite cheap from CPC or Amazon- your temp bodge can be to connect the relay coil to your existing dhw controller and power the heater from the 20A contacts (use an FCU if you want or use adequate sized cable and an unfused connection unit)
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I would agree with that, only worth considering if on peak/off peak supplies.
Here is a photo of the socket in my airing cupboard. Only the immersion heater is ever plugged in here. What could I fit in its place so that I could safely time the heater to come on and off? It is wired into the upstairs ring (before I moved in) but there are just a few radios and computers that use that ring so it's never overloaded.
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https://www.tlc-direct.co.uk/Products/SMFST77.html I have this, it's a fused spur so replaced the socket on the ring.
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Click on the instruction booklet...
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