Immersion Heater Replacement in St John's
A homeowner in St John's reported that their hot water was only lukewarm, even after running the immersion heater for the usual amount of time. The water had been gradually getting...
Response time
Booked in 2 days
Time on site
2.5 hours
Cost range
£195
Warranty
12 months
The Problem
A homeowner in St John's reported that their hot water was only lukewarm, even after running the immersion heater for the usual amount of time. The water had been gradually getting cooler over several weeks. The top immersion heater seemed to be working but the water was not reaching full temperature.
The property had a vented hot water cylinder with two immersion heaters — top and bottom. The bottom immersion was set to heat overnight on an economy tariff, and the top was used for daytime top-ups.
The Diagnosis
We tested both immersion heater elements with a multimeter. The top element tested correctly and was heating. The bottom element showed an open circuit — the heating coil had burned out and was no longer producing heat. This explained why the water was only lukewarm — only the top element was working, heating only the top third of the cylinder.
The cylinder thermostat was functioning correctly. The failed bottom element had likely been degrading for some time, which is why the water temperature had been gradually decreasing.
The Repair
We isolated the electrical supply at the consumer unit, isolated the water supply, and drained the cylinder down to below the bottom immersion heater level. The old 27-inch immersion heater was removed using an immersion heater spanner.
A new 27-inch immersion heater element was fitted with a new fibre washer, the cylinder was refilled and vented, and the electrical connections were remade. The supply was restored and the element was tested under load to confirm it was heating the full cylinder.
Diagnosed burnt-out bottom immersion element
Drained cylinder and replaced failed element
Refilled, reconnected and tested under load
Outcome & Advice to the Homeowner
Full hot water was restored — the cylinder now heated completely, providing a full tank of hot water at the correct temperature. The homeowner was pleased to have resolved the gradual decline in hot water performance.
We recommended setting both cylinder thermostats to 60°C and checking the immersion elements annually for signs of scaling, which can reduce efficiency and lifespan.
Job Summary
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