BoilerFaultCodesYour boiler has lost its connection to the hot water tank sensor, meaning it cannot tell how hot your water is and may stop providing it.
This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.
Technical description: Short circuit in tank sensor | NTC defective, earth leak/short circuit in cable loom, damp plug connection
What causes this fault?
This fault occurs when the boiler can no longer communicate with the temperature sensor inside your hot water cylinder. The most common reason is that the sensor has developed an internal electrical failure or the wiring connecting it to the boiler has become loose, damaged, or damp. Because the boiler doesn't know how hot the water is, it stops heating the tank to prevent overheating.
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 F.13 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Vaillant ecoMAX 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.