F.78 Medium
Your boiler is having trouble communicating with an external temperature sensor used for your hot water, meaning the system doesn't know how hot the water is.
Technical description: Interruption to DHW outlet sensor at external controller
Typical repair cost: £90-180 (including labour)
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Protect yourself from future repair bills
A boiler cover plan would cover faults like F.78 — no call-out fees, no surprises.
*Affiliate links — we may earn a commission at no extra cost to you. Prices shown are starting prices.
Parts commonly replaced
- DHW Outlet Sensor
- Wiring Harness
- External Controller (VRC 700/720)
*Affiliate links — we may earn a commission at no extra cost to you.