BoilerFaultCodesYour boiler has shut down because the water returning from your radiators is getting too hot, indicating a potential blockage or pump issue.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: The heating return thermistor is detecting an excessive temperature.
What causes this fault?
This fault occurs when the water traveling back from your radiators is nearly as hot as the water leaving the boiler, which prevents the system from cooling down properly. Typically, this happens because the water isn't moving through the pipes fast enough due to a failing pump or a buildup of sludge creating a blockage. It can also be triggered if the sensor responsible for monitoring these temperatures has become faulty and is sending incorrect data to the control board.
This issue often surfaces during the first cold spell of autumn when the heating system is turned on after being dormant all summer, which can cause internal pump parts to seize.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like 19 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Glow-worm Energysaver Combi 2 80 100 is discontinued — time for a new one?
Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
Affiliate links — we may earn a commission at no extra cost to you.