Immersion heater

[Scarlett]

Is it okay to leave an immersion heater on constant, so you get constant hot water? My tenant is doing this because he believes that it is cheaper than heating the water for, say, 2 hours every day. As a result the immersion keeps shorting the system as it overheats, and now the thermostat needs replacing.
Is he right? Or is he misusing it?!

[scotman]

re cheaper; this depends on amount of water used per day, the level of insulation on the tank and the setting of the thermostat.
The thermostat should cut out at set temperature so I don't understand what you mean by 'overheating' I f it was shorting the system it probably needed replacing anyway

[eltelioni]

As scotman says, the immersion heater is faulty and you need to replace it. It should function correctly when left on continuously, regardless of the economics.

By the way, your tenant is wrong. It is impossible for it to be cheaper to leave it on continuously.

[eltelioni]

I can justify that statement.

The immersion heater replaces heat lost by using the hot water for baths/showers/washing up/etc. It also replaces the heat lost from the water stored in the tank. No matter how well insulated the tank is, it will lose heat. The rate of heat loss is proportional to temperature (Newton's Law of Cooling), therefore the rate of heat loss reduces as the temperature in the tank falls. Leaving the immersion on continuously keeps the temperature high and therefore keeps the rate of heat loss relatively high.

Unless your tenant is smarter than Newton, he is talking out of his bottom.

[Scarlett]

Haha great thanks, that is what I thought! The thermostat is being replaced, as it clearly wasn't keeping the water at a set temperature, and was instead allowing it to get over-hot and short the system.

I am glad you think he is talking nonsense- I have told him not to keep it on the whole time. Gah!

[knobbynonut5]

A thermostat in an immersion that is faulty and lets the water overheat would not blow the fuse or mcb.

Even though the stat might need replacing it would be more likely that the element in the immersion is corroded and faulty and needs replacing.

[eltelioni]

I agree with knobby. Replace the whole thing. It is not worth the risk.