Common problems guide

The most common Evo boiler problems

The faults we see most often across the Evo range — with plain-English causes, what to check first, estimated repair costs, and whether it's a DIY job or needs a Gas Safe engineer. Based on fault-code data across 2 Evo boiler models.

13 unique codes
2 models covered
5 DIY-safe (top 8)
8 engineer needed

The most common Evo faults

01
H9/L9 High DIY-safe

Your boiler has shut down because the internal water temperature has become too hot, causing it to lock out for safety.

What to try first

Check that all radiator valves are fully openEnsure the boiler pressure is between 1.0 and 1.5 barTry resetting the boiler once the unit has cooled down

Est. cost
£120-£350
Parts
Circulation Pump, Overheat Thermostat, Main Heat Exchanger
Full guide for HE C22/30 H9/L9
02
L E High DIY-safe

Your boiler has failed to ignite after several attempts, meaning the system cannot provide heating or hot water until it is reset.

What to try first

Check that your gas supply is turned on (check other gas appliances like your hob).Press and hold the 'Reset' button for five seconds.If the boiler has been off for a long time, repeat the reset process up to three times to clear air from the pipes.

Est. cost
£100-350
Parts
Ignition Electrode, Flame Sensing Probe, Gas Valve
Full guide for HE C22/30 L E
03
L A High DIY-safe

Your boiler has failed to ignite after several attempts, meaning you will not have any heating or hot water until the system is reset or repaired.

What to try first

Check that your gas emergency control valve is in the 'on' position and you have credit on your meter.Press the 'Reset' button on the boiler control panel for two seconds.Ensure the condensate pipe (the plastic pipe leading outside) is not frozen if it is currently very cold weather.

Est. cost
£120-£350
Parts
Ignition Electrode, Gas Valve, Flame Sensing Electrode
Full guide for HE C22/30 L A
04
LA/HA High DIY-safe

Your boiler has become too hot and has shut down as a safety precaution to prevent damage.

What to try first

Check that all radiator valves are fully openEnsure the boiler pressure is between 1.0 and 1.5 barWait for the unit to cool down below 50°C before attempting to reset

Est. cost
£120-350
Parts
Circulation Pump, Heat Exchanger (de-sludging), Overheat Thermostat
Full guide for HE C22/30 LA/HA
05
93 High DIY-safe

Your boiler is struggling to detect the flame it has lit, causing the system to shut down for safety.

What to try first

Check that your gas emergency control valve is open and you have credit on your gas meterTest if other gas appliances in the home, such as a hob, are working correctlyPress the reset button once to see if the boiler restarts

Est. cost
£100-£280
Parts
Flame sensing electrode, Ignition lead, Gas valve
Full guide for HE C22/30 93
06
H E High Engineer

Your boiler has detected an internal communication error between the main control board and its display or ignition system, preventing it from starting up.

Est. cost
£180-350
Parts
Main PCB, Internal Wiring Loom
Full guide for HE C22/30 H E
07
H 9 High Engineer

Your boiler has detected an internal communication error between its electronic control boards or an incorrect configuration.

Est. cost
£180-450
Parts
Main PCB, User Interface Board, Wiring Harness
Full guide for HE 12 H 9
08
L 9 High Engineer

Your boiler has overheated, causing it to shut down automatically for safety.

Est. cost
£120-350
Parts
Circulation pump, Overheat thermostat, Main heat exchanger (flushing needed)
Full guide for HE 12 L 9

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