Baxi Luna Duo-tec E09 — Return Temperature Too High
E09
Return temperature too high. Sensor fault. Sensor not/poorly connected. No circulation. Check the wiring. Replace the sensor if necessary. Purge the air in the heating system. Check for water circulation (direction, pump, valves). Check the water pressure. Check that the sensors are operating correctly. Check that the sensors have been correctly fitted. Check the cleanliness of the heat exchanger. The table classifies it as Lockout (manual reset).
Applies to
This low-water or pressure protection code is displayed by the Duo-tec MP control on Luna Duo-tec MP heating models (1.70MP, 1.110MP and 1.33GA/1.48GA heating variants), as documented in Luna Duo-tec 1.70MP / 1.110MP Installation & Operation Manual (Canada, EN-FR), I&O 7703477.01 (7703477.01). Codes can differ between controller generations, so always check the manual that matches your unit.
- Baxi Baxi Luna (North America)
- Baxi Duo-tec Compact 30GA
- Baxi Luna Duo-tec 40GA
- Baxi Luna Duo-tec 60GA
- Baxi Luna Duo-tec 1.33GA
- Baxi Luna Duo-tec 1.48GA
- Baxi Luna Duo-tec 1.70MP
- Baxi Luna Duo-tec 1.110MP
Controller: Duo-tec MP control. Source manual: 7703477.01 (2018-03).
Why a code is not a diagnosis
A water-pressure or low-water code can mean a genuine leak or empty system, a failed expansion tank, a faulty fill valve, or a sensor problem. The appliance does not distinguish these.
Safe things to observe
- Read the pressure gauge and compare it with the normal cold-system pressure your installer set.
- Look for drips or wet spots near the appliance, pipes and the relief-valve discharge.
Do not
- Do not keep re-pressurizing a system that keeps losing water.
- Do not cap a relief-valve discharge pipe.
How professional service helps
- A technician finds and repairs the leak, checks the expansion tank and fill assembly, and verifies the sensor circuit.
Where ROMA provides on-site service
On-site service is currently offered in Greater Vancouver, BC, including Vancouver, Burnaby, Richmond, Surrey, Coquitlam, North Vancouver, West Vancouver, New Westminster, Port Coquitlam, Port Moody, Delta, Langley, Maple Ridge, Abbotsford, Chilliwack, White Rock, Pitt Meadows, Tsawwassen, Anmore, Lions Bay, Belcarra, Bowen Island, Mission. Everything else on this site is reference information you can use anywhere in Canada.
Parts and service
Parts commonly involved
These parts appear in the documented text for this alert. A code reports a condition, not a failed part — a technician confirms the cause by testing before anything is replaced.
Heat exchanger
The heat exchanger is where a boiler transfers heat from the burner flame to the water that heats your home.
What a technician checks →Boiler sensors (thermistors)
Boiler sensors are small temperature probes, usually thermistors, that tell the control how hot the water and flue gases are so it can fire safely…
What a technician checks →
Service for this alert
- Gas Boiler Repair
Licensed gas technicians from ROMA Heating & Cooling diagnose and repair residential and light-commercial gas boilers across…
- Emergency Boiler Repair
Priority gas boiler repair for homes and buildings in Greater Vancouver with no heat, no hot water, a locked-out boiler or a leak.
- Gas Boiler Replacement
ROMA replaces old, failed or inefficient gas boilers in Greater Vancouver, handling removal, venting and gas-supply changes,…
Every boiler part explained — what it does, how it fails and what a technician checks.
Documented for Baxi Baxi Luna (North America).
Frequently asked questions
Can I clear this code myself?
Clearing a code without fixing its cause usually just brings it back. Note the code, check the safe items on this page, then call a licensed technician. If your appliance manual describes a user reset for this exact code and it stays away, no call may be needed.
Boiler locked out? Call with the alert text ready.
The brand, model and this alert are passed along when you request service online, so the technician arrives prepared.
On-site service in Greater Vancouver, BC. ROMA lists “Open 7 days” on its site; call to confirm same-day availability.
Sources and verification
- Luna Duo-tec 1.70MP / 1.110MP Installation & Operation Manual (Canada, EN-FR), I&O 7703477.01 · 7703477.01 · accessed September 9, 2026
Facts checked September 9, 2026. Last updated September 9, 2026. Technical reviewer: not yet assigned.