Temperature and pressure release valves

These help the tank breathe when it reaches temperature of 90 degrees and
over. This if ascertained is no longer functional will have to be replaced in order
to protect the tank. It is advisable that if you are going to stay away for a
prolonged period of time i.e. holiday you get a tarpaulin and cover the heater.
If the water is not used, the temperatures build up open the temperature
release valves for prolonged periods thus increasing your water bill.