BoilerFaultCodesYour boiler is having trouble 'talking' to your solar panels or an additional heating control part, which might prevent those specific systems from working correctly.
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: Communication fault: Solar control module or extension module
What causes this fault?
This fault occurs when the boiler's main computer loses its digital connection with the supplementary units that manage your solar thermal panels or extra heating zones. It is usually caused by a loose wiring connection or an internal electronic failure within the expansion module itself, meaning the boiler can no longer send or receive instructions from those parts of your system.
DIY fix possible
Locate the power switch (fused spur) for the boiler.Turn the power off, wait for 30 seconds, and turn it back on to see if the connection resets.Check if any external solar controllers or expansion boxes have lost power or been unplugged.
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 C2 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.