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Most-searched boiler fault codes

The fault codes UK boiler owners actually look up — ranked by what's most searched on the site. Each entry links to the full plain-English explanation, repair cost estimate, and severity.

#	Code	What it means	Severity	Searches
1	591 Ariston E-Combi One	Your boiler has detected a communication error with its internal combustion control system, meaning it cannot safely regulate the burner. ~£150-300	High	0 clicks 1 impressions
2	H.00.42 Baxi 400 Combi 2	Your boiler has stopped working because it cannot correctly detect the water pressure inside the system. ~£140-£220	High	0 clicks 1 impressions
3	H.00.42 Baxi 600 Combi 2	Your boiler has stopped working because it cannot correctly detect the water pressure, likely due to a faulty internal sensor or a broken connection. ~£140-£220	High	0 clicks 1 impressions
4	H.00.42 Baxi 800 System 2	Your boiler has stopped working because it cannot correctly detect the water pressure, likely due to a faulty internal sensor or a broken connection. ~£140-£220	High	0 clicks 1 impressions
5	S.31 Heatline Monza	Your boiler is currently set to only provide hot water and will not heat your radiators.	Low	0 clicks 1 impressions
6	Service Due Ideal Logic Max Heat 2	Your boiler is simply reminding you that its annual safety check and maintenance visit is now due. ~£80-120	Low	0 clicks 1 impressions
7	4.11 Ideal Vogue Gen2 Combi	Your boiler has detected that there is not enough water in the system to operate safely, causing it to shut down to prevent damage. ~£0-120	High	0 clicks 1 impressions
8	4.15 Ideal Vogue Gen2 Combi	Your boiler is providing central heating as normal, but it has stopped producing hot water when you turn on your taps. ~£180-350	Medium	0 clicks 1 impressions
9	PCB REPLACED Ideal Vogue Gen2 Combi	Your boiler has recently had its main circuit board replaced and simply needs to be rebooted to confirm the change.	Low	0 clicks 1 impressions
10	E030 Navien NCB CE	Your boiler is detecting an issue with water flow or heat levels, which could mean dangerous air or gas is trapped inside where it shouldn't be. ~£150-400	Emergency	0 clicks 1 impressions
11	Pulse Red (3 flashes) Potterton Envoy	Your boiler has detected that it is dangerously overheating and has automatically shut itself down to prevent internal damage. ~£180-350	Emergency	0 clicks 1 impressions
12	E42 Potterton Powermax HE	Your boiler's computer brain has encountered a serious internal error and can no longer control the heating or hot water safely. ~£350-£550	High	0 clicks 1 impressions
13	S.13 Vaillant ecoTEC plus 938 VUI GB 386/5-5 A	Your boiler is currently just starting the process to heat your water, so it is working normally and does not have a fault.	Low	0 clicks 1 impressions
14	S.57 Vaillant ecoTEC pro	Your boiler is temporarily pausing to perform a routine internal diagnostic check and will resume normal operation on its own shortly.	Low	0 clicks 1 impressions

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