Immersions puzzling now I have monitor. Can anybody help explain please?

merrylegs61

Me again (sorry!)
Now have energy monitor and am having a play around with the immersions to see the readings. Two immersions to heat my large hot water tank. With both switched off, my energy monitor currently reads 2p. With both immersions on, that jumps to 41p. If I switch the immersion heater for the top half of the tank off, the reading only drops to 40p. But if I leave the immersion on for the top half and switch the immersion off for the bottom half, the monitor reading stays at 2p. Am I right in assuming that means there is something up with the immersion for the top half of the tank or is that too simple/dense?

matelodave

Ok, stop looking at money look at kwh which is more meaningful

If you are all electric on an e7 tariff then usually the bottom heater will only come on during the night (under control of a timer or the e7 meter). The top heater will be connected to the non-switched peakrate supply and so will come on when ever you switch it on an off.

So you should see - both off = low level consumption, fridge, freezer, Sky box and anything else. Turn the top one on and you should see a load of around 3kwh (which is roughly equal to your 40p). If you turn the bottom one on during the day, nothing should happen because it shouldn't come on.

If you do it later (after midnight or before 7 am) you should see 3kw from the bottom heater and 3kw from the top one = 6kw however if the heater has been on all night, the tank should be hot, so you may not see any drain from either heater if you try it out first thing in the morning.

merrylegs61

Not on E7 though?

Talldave

Possible then that the top immersion has died (assuming you did your test with the tank cold). There's a remote possibility that the place is wired for E7 even though you're single rate, however I think it's unlikely because as @matelodave pointed out, the off-peak immersion would be the lower one.
Ditto on the monitoring in Watts method!

merrylegs61

Place was wired for e10. I had meter replaced last year with single rate. Nobody had every explained (and I asked plenty!) how water was heated when e10. Presumably, guy bunged in new meter but wiring remains as was? In which case, what now happens with immersion and water tank? 

Talldave

If you want to do the detective work without calling in an electrician,  you could get a mains voltage detector pen that lights an led when it detects mains. You could then test if there's mains in the cable of the immersion that doesn't work.  However,  whatever the outcome you'll need an electrician to either replace the immersion or trace the lack of power to that circuit (assuming you want to do anything about it!). The top immersion should give a cheaper top up of the top of the tank.

merrylegs61

Thank you 

ianto11

Talldave said:

If you want to do the detective work without calling in an electrician,  you could get a mains voltage detector pen that lights an led when it detects mains. You could then test if there's mains in the cable of the immersion that doesn't work.  .

The thermostat inside the head may be similar to these and they have a thermal cutout,  marked as "safety" on this one, so there would still be voltage present on the 2 terminals, just not being passed to the element by the thermostat. 
If you switch off the power to the immersion, the cutout can be reset by pushing a small flat blade screwdriver into the "safety" hole and you should hear an audible click.