heating
Immersion heaters and hot water
Replacing an immersion element costs £150 to £300 including the part. Before paying for one, check the thermostat: it fails more often than the element does, it costs a fraction as much, and the symptom is identical.
What this covers
What it costs. An element replaced is £150 to £300 including the part. Full cost breakdown.
What the job covers
- Replacing a failed immersion element
- Fitting twin element cylinders on off peak supply
- Wiring immersion timers and boost switches
- Replacing the thermostat rather than the element
- Upgrading cable and isolation to current standards
What is involved
An immersion heater is an element on a thread in the side or the top of a cylinder, with a thermostat pushed down a pocket inside it and a cover over the terminals. When there is no hot water the fault is one of four things, in rough order of likelihood: the thermostat, the element, the switch or timer feeding it, or the circuit itself. Testing takes minutes and tells you which, and it is the difference between a £40 part and a £200 job.
Getting a seized element out is where the time goes. They sit in hard water for years and the thread bonds to the boss. A proper immersion spanner and patience usually win; occasionally the element shears and the cylinder is finished, which is worth knowing before starting on a cylinder that owes nothing to anybody. The tank has to be drained below the element first, and on an unvented cylinder that is a different procedure with its own isolation.
Two elements in one cylinder is an off peak arrangement rather than a redundancy. A long element near the bottom heats the whole tank overnight on the cheap rate, and a short one near the top heats the last third for a quick boost during the day. If only the top of the tank ever gets hot, the bottom element or its supply has failed, and the house has been running on the expensive one for a while without anybody noticing.
Choosing someone for the job
Ask for the thermostat to be tested before the element is condemned, because it is the commoner fault and the cheaper part. Ask what happens if the element shears in the boss. On an unvented cylinder, ask whether they hold the qualification for it. Ask which of the two elements is being replaced if the cylinder has two.
Common questions
No hot water. Is it the element?
It might be, and the thermostat fails more often. Both produce the same symptom and testing distinguishes them in minutes. Ask for that test before agreeing to a replacement element.
Why does only the top of my tank get hot?
A twin element cylinder where the lower element, its thermostat or its off peak supply has failed. The top element is covering, which works and costs a good deal more to run because it is on the day rate.