BoilerFaultCodesWhat the manual says
Manufacturer manualOverheating protection on – primary heat exchanger has responded
From this model's manual
Verified against the Vaillant Ecotec Combi installation & service manual, page 47.
What causes this fault?
This fault occurs when a dedicated safety fuse inside the main heat exchanger melts because the component has reached an unsafe temperature. The most common reason is a buildup of limescale or sludge that restricts water flow, causing the metal to overheat and permanently blow the fuse. Unlike a standard overheat, this is a one-time safety device that cannot be simply reset.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register →
Boiler cover options
Avoid the next call-out bill
A cover plan would handle faults like F.76: no call-out fees, no surprise bills.
Approved partner
Get a quote →
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Affiliate links. We may earn a commission at no extra cost to you.