BoilerFaultCodesYour boiler is slowing down its performance because it has detected that the gas pressure coming into the unit is too low to run at full power.
This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.
Technical description: Capacity reduction for detected low gas inlet pressure – check the CO2 calibration values.
What causes this fault?
This fault occurs when the boiler detects that the gas supply pressure is insufficient to maintain the high heat output it is trying to achieve. It is often caused by a bottleneck in the pipework or a gas valve that isn't opening fully, forcing the system to reduce its power to prevent the flame from failing entirely. In some cases, it can also be triggered if the gas meter's regulator is faulty or if the boiler's internal sensors are miscalibrated.
This issue is most frequent during the coldest months when high demand across the local gas network and your own heating system can cause a noticeable drop in inlet pressure.
DIY fix possible
Check that your gas emergency control valve (next to your meter) is fully openIf you have a pre-payment meter, check that you have sufficient creditCheck if other gas appliances, like a hob, are working correctly to rule out a grid supply issue
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
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A boiler cover plan would cover faults like E84 — no call-out fees, no surprises.
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