--- title: "Heat Pump Error Codes: Mitsubishi, Daikin, Vaillant | Appian" description: "Common Mitsubishi, Daikin and Vaillant heat pump error codes decoded — which faults you can reset yourself and which need an engineer." lang: en-GB json-ld: | [ { "@context": "https://schema.org", "@type": "Article", "headline": "Heat Pump Error Codes: Mitsubishi, Daikin, Vaillant", "description": "Seeing a fault code on your heat pump controller? We decode the most common error codes across major brands and explain which ones you can reset yourself and which need an engineer.", "datePublished": "2026-03-01", "author": { "@type": "Person", "name": "Craig Ball" }, "publisher": { "@type": "Organization", "name": "Appian Heat Pumps", "url": "https://www.appianheatpumps.com" }, "mainEntityOfPage": { "@type": "WebPage", "@id": "https://www.appianheatpumps.com/blog/heat-pump-error-codes-explained" } }, { "@context": "https://schema.org", "@type": "BreadcrumbList", "itemListElement": [ { "@type": "ListItem", "position": 1, "name": "Home", "item": "https://www.appianheatpumps.com/" }, { "@type": "ListItem", "position": 2, "name": "Blog", "item": "https://www.appianheatpumps.com/blog" }, { "@type": "ListItem", "position": 3, "name": "Heat Pump Error Codes: Mitsubishi, Daikin, Vaillant" } ] } ] --- [ Special Offer Air Conditioning Fully Installed from £1,100 → ](/contact) 12 Appian Way, Chineham, Basingstoke, RG24 8BH Fastest reply → [07481 552059](tel:07481552059)| [01256 672332](tel:01256672332) [![Appian Heat Pumps](/assets/logo-DXHDe5EY.png)](/) Services Service Areas [About](/about)[Our Work](/our-work)[Blog](/blog)[Reviews](/reviews)[Contact](/contact) Call now — fastest reply [07481 552059](tel:07481552059)[Landline: 01256 672332](tel:01256672332) [Request Estimate](/contact) [Call 07481 552059 Fastest reply ](tel:07481552059)[Get Estimate](/contact) 1. [Home](/) [Blog](/blog) Heat Pump Error Codes: Mitsubishi, Daikin, Vaillant Troubleshooting # Heat Pump Error Codes: Mitsubishi, Daikin, Vaillant Seeing a fault code on your heat pump controller? We decode the most common error codes across major brands and explain which ones you can reset yourself and which need an engineer. By Craig Ball 1 March 2026 7 min read ![Heat Pump Error Codes: Mitsubishi, Daikin, Vaillant — featured image](/assets/blog-error-codes-D9iq7kzI.jpg) ## Mitsubishi Ecodan Error Codes The most common Mitsubishi Ecodan fault codes we encounter: E1 (outdoor-indoor communication error) — often a loose cable connection. E6 (inverter compressor overcurrent) — can indicate a failing compressor or refrigerant issue. E8 (inverter compressor overload) — often caused by restricted airflow or high ambient temperatures. P1 and P8 codes relate to pressure sensor faults. These can sometimes be resolved by a system reset, but if they recur, the pressure sensor or refrigerant charge needs checking as part of a proper [heat pump repair](/services/heat-pump-repair) by an F-Gas certified engineer. ## Daikin Altherma Error Codes Daikin systems display errors as alphanumeric codes. Common ones include: U0 (refrigerant shortage or metering device fault), 7H (outdoor fan motor fault), E7 (outdoor fan motor locked), and AH (air purge error). The AH error is frequently seen on new installations where the refrigerant lines weren't properly evacuated. Daikin errors beginning with 'L' typically relate to the hydraulic module and can often indicate water flow issues rather than refrigerant problems. Check that valves are open and the circulation pump is running before calling an engineer. ## Vaillant aroTHERM Error Codes Vaillant displays fault codes with an 'F' prefix. F.20 to F.28 relate to temperature sensor faults. F.61 and F.62 indicate gas valve faults (relevant for hybrid systems). F.75 relates to water pressure sensor issues — often resolved by repressurising the system. The Vaillant aroTHERM can be particularly sensitive to water flow rates. Error codes related to high-pressure faults often trace back to partially closed valves, air locks, or an undersized buffer tank rather than a refrigerant issue. ## When to Reset vs When to Call As a general rule: if a fault code appears once and clears after a reset, monitor the system for recurrence. If the same code appears twice within a week, call an engineer. If a code relates to compressor overcurrent, high pressure, or refrigerant shortage, do not reset — call our [emergency repair line](/services/emergency-repairs) immediately. Never repeatedly reset a heat pump that keeps faulting. Each fault event can cause additional stress on components, particularly the compressor. Three resets and the same fault should be your maximum before booking a [diagnostic repair visit](/services/heat-pump-repair). Craig Ball Founder & Lead Engineer · F-Gas Certified · 15+ Years Craig has installed, serviced, and repaired heat pumps across Hampshire and the south for over 15 years. Articles are written from real installation experience, not marketing copy. ### Related Services [Heat Pump Repair](/services/heat-pump-repair)[Heat Pump Servicing](/services/heat-pump-servicing)[Heat Pump Installation](/services/heat-pump-installation)[System Optimisation](/services/commissioning-optimisation) [ Previous Air Source Heat Pump Running Costs UK 2026 ](/blog/air-source-heat-pump-running-costs-uk)[ Next Swimming Pool Heat Pump Sizing Guide ](/blog/swimming-pool-heat-pump-sizing-guide) ## Need Help With Your Heat Pump? If this article describes your situation, we can help. Call Craig directly or request a free estimate. 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