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i have an immersion heater that only heats half the tank. i have less than one baths worth of hot water and despite a new thermostat and new heating element, I can't get more water from it. The plumber has put a stick down the tank to see if the bottom half is full of scale but it seems to be ok. So - i should get more water but i don't. Would anyone know why?
many thanks.

The immersion heater will only heat water above it. Sometimes you get two heaters in one unit one goes deeper than the other from the top of the tank and you can select short one for normal domestic and long one before having a bath. Some times two completely separate units are fitted in the side of the tank. As well as the heaters they also have thermostats which slide down a tube called a pocket inside the immersion heater if this is wrong length it can switch them off too early and also sometimes the tank is too small to fill bath and it relies on the temperature being set high and cold water being added. Also sometimes there is a pump that circulates the water so hot water comes straight away and no need to run off cold this also ensures whole tank warms up if switched off then you will get reduced amount of water. The latter is normally only with big houses.
As to which one is problem in your case, I will guess on wrong immersion heater or thermostat fitted. 11 inch and 27 inch seem to be common sizes so how far down the tank does it heat? But there are also 14", 30" and 36" do any of those lengths seem to match how much heats up?

hey, big thanks for the reply. the tank heating element is 27inches which seems to go a fare way down the tank itself. its such a puzzle! and my plumber chap can't figure it out. Perhaps the only way is to fit a longer element?

Is it heating 27 inches down the tank? maybe wrong length thermostat? You can work out what you should get. If your tank is 900mm diameter and 27 inch = 685 down that's 0.436 Cubic meters or 436 Litres or 96 gallons. The bath harder 1.5 meters long and 0.55 wide because of curves I will consider it as 0.45 wide but looking at some where around 60 gallons to fill bath which should mean you would have no problem but London government site says 90 litres i.e. 20 gallons or 10 bucket full which buy time you realise there is a body in the bath as well is quite likely. So you should fill a bath without a problem unless your very small and bath very large. I will guess wrong length thermostat?

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