BoilerFaultCodesYour boiler has detected very cold temperatures and has automatically turned itself on to prevent the internal pipes from freezing.
This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.
Technical description: Displayed when the water temperature within the boiler is below 5°C; the boiler will fire until a return temperature of 10°C is reached (Frost Protection).
What causes this fault?
This occurs when the sensors inside your boiler detect that the water temperature has dropped to a level where there is a risk of freezing. It is a built-in safety feature designed to protect the internal components and heat exchanger from cracking. The boiler will automatically run for a short period to circulate and warm the water until it reaches a safe temperature.
This status is almost exclusively seen during the winter months when external temperatures drop near or below freezing.
DIY fix possible
No action is required as this is a normal safety function.Ensure your gas supply is active so the boiler can maintain the temperature.Check that any external pipes are correctly insulated to prevent future freezing.
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 C — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Potterton Envoy System 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.