The immersion element on this cylinder had stopped working.
It is the white cover near the bottom of the cylinder in the photograph, with the cable coming out of it. Behind the cover is the head of the element, and the rest of it is out of sight: a long electric heater that screws into the cylinder and sits in the water, with a thermostat in its head that switches it on when the water cools and off again when it is hot enough. When an element goes, that side of the cylinder stops heating, and in a house where it is the only thing heating the water, the hot taps run cold.
Plumbing and electrical, both on the one job, and that is why it is worth showing.
Two trades, one part
An immersion element is the clearest case there is of a fault sitting on the line between the two trades. The electrical half is everything up to the cover: the switched supply and the cable, the thermostat, and the testing that tells you whether it is the element that has failed, the thermostat, or the supply feeding them, which is ordinary fault finding and the reason the meter comes out before the spanner does. The plumbing half is everything behind it. The element is screwed into a boss on the cylinder with a seal, in a cylinder full of water, and this one is near the bottom, so getting the old one out means isolating the cylinder and draining it down below the element first. The new one goes in on a new seal, the cylinder is refilled and the air let out of it, the boss is watched for a weep, and only then does the electrical half come back, with the thermostat set and the supply proved before the cover goes on. A firm that carries one of those trades can do half of it. Then it is a second call to a second firm, with the cylinder sitting half empty in between, and that is the reason this firm carries both.
In the frame
The red cap at the top left is the relief valve, on the side of the cylinder. Below it on the copper is the tundish, the black fitting with the gap in it, which is where anything that valve lets go shows up so somebody sees it. The brass fitting halfway up is a second boss on the cylinder with a cap on it, and the green circle at the top is the maker’s label.
The job was the white cover at the bottom.
Hard water
An element lives in the water it heats, and where the water is hard, scale builds up on it over time. It is on our boiler page too, because hard water does the same thing to a boiler.
One number
Ring 07546 185778 and say what has stopped: the hot water, the heating, or both. It is the same call either way.
