Hi all, i had a new unvented cylinder fitted on Monday and the gas boiler side of things works beautifully, but the immersion heater doesn’t seem to act as I would expect.
It heats the tank to around 40C (measured at the thermostat pocket, but also roughly confirmed by seeing where the cylinder stat clicks when rotated). Then it goes into a cycle of being on for a few mins, then off for a few mins etc, but with little temperature rise.
We have an EV tariff and so get cheap electricity at 5.5p/kWh between 20.30 and 01.30, so heating cylinder this way is much cheaper than using gas at 8.9p/kWh. We are also having solar fitted in a few weeks, so will be planning to use the immersion to heat the water as much as possible, so want to make sure it’s working right.
The immersion is a Thermowatt Alloy 800 3kW, with an RTS-3 thermostat. I have this set to maximum (which should be 65C according to specs).
Some photos:




Here is a readout from our smart meter from 20.30 to 22.30, showing the immersion cycling repeatedly, despite cylinder temp only being ~40C:

Any thoughts appreciated before I call the installer back. Duff immersion thermostat perhaps?
Thanks!
It heats the tank to around 40C (measured at the thermostat pocket, but also roughly confirmed by seeing where the cylinder stat clicks when rotated). Then it goes into a cycle of being on for a few mins, then off for a few mins etc, but with little temperature rise.
We have an EV tariff and so get cheap electricity at 5.5p/kWh between 20.30 and 01.30, so heating cylinder this way is much cheaper than using gas at 8.9p/kWh. We are also having solar fitted in a few weeks, so will be planning to use the immersion to heat the water as much as possible, so want to make sure it’s working right.
The immersion is a Thermowatt Alloy 800 3kW, with an RTS-3 thermostat. I have this set to maximum (which should be 65C according to specs).
Some photos:




Here is a readout from our smart meter from 20.30 to 22.30, showing the immersion cycling repeatedly, despite cylinder temp only being ~40C:

Any thoughts appreciated before I call the installer back. Duff immersion thermostat perhaps?
Thanks!