Immersion heater question

amstel2

Hello

I get hot water from an electric immersion heater/tank that was installed about 5 years ago (the old one was over 50 years old & had given excellent service but finally stopped working). The chap that installed it said the most economical way to use an immersion is to leave it on all the time as it costs a lot more to heat a tank of water from cold than to let the thermostat maintain the temp.

I tested what he said, I left it on for a month & the following month put it on for about an hour morning & night as I needed it. To be honest going by the meter readings it was slightly more economical leaving it on as he said. With the added connivance of constant hot water.

However, I have now heard it can be dangerous to leave an immersion on all the time in case the thermostat fails & the the water would keep getting hotter which could cause the tank to explode. Is this right?

Whats puzzling me is that about 2 years ago the water stopped heating up was always cold & the culprit then was a faulty thermostat that i had to replace. So in my experience if a thermostat stops working the water stays cold.

So whats right. Any ideas please.

Thanks

vaio

thermostats can fail on or off, luck of the draw really whether you end up with cold or boiling water.

modern heaters/thermostats have an additional "high limit" 'stat which will cut the power if the primary 'stat fails closed. The "high limit" 'stat doesn't self reset so it it operates then the power stays off until you repair/reset it manually

I_have_spoken

which could cause the tank to explode. Is this right?

No. The tank is vented, so steam/boiling water would get return to the expansion tank, usuall in the loft

Jonesya

Cost-wise - are you on an Economy 7 electricity tariff?

If you are, then you really want the main immersion heater on a timer to come on overnight using the cheap rate electricity.

Another thing to check is the insulation on the tank, fitting a tank jacket to reduce the heat loss.