New Yorker Boiler · Error codes
New Yorker GHE-II Combi E04 — Supply High Limit
E04
Supply High Limit. Supply temperature is higher than 210F (99C), or the preferred outlet/flow high limit, which locks the boiler out; listed causes are air in the system, a system pump/thermostat/zone valve/panel problem, piping problems, a boiler pump problem, a three-way valve not functioning properly, a heating zone too small for the installed boiler, and a header sensor not sensing temperature. The table classifies it as Lockout.
Applies to
This overheating code is displayed by the GHE-II Combi control (H hold/warning and E lockout codes) on GHE-II Combi models (GHE2C-136B, GHE2C-200), as documented in GHE-II High Efficiency Combi Boiler — Installation, Operating & Service Instructions (English), doc 110329-10 (11/25), Section 19 Table 19-5 (110329-10). Codes can differ between controller generations, so always check the manual that matches your unit.
Controller: GHE-II Combi control (H hold/warning and E lockout codes). Source manual: 110329-10 (2025-11).
Why a code is not a diagnosis
An over-temperature code protects the heat exchanger or venting; it does not reveal whether the cause is low water flow, a failed pump, trapped air, fouling or a sensor fault.
Safe things to observe
- Note the code and whether rooms or hot water are still working.
- If you see steam, melted wiring or smell burning, switch the appliance off at its service switch and call a technician.
Do not
- Do not reset the appliance repeatedly while the cause is unknown.
- Do not remove covers or bypass any high-limit device.
How professional service helps
- A technician checks pump operation, flow, system pressure and the cleanliness of the heat exchanger.
- Combustion and safety devices are verified with an analyser and the manufacturer's procedure after any repair.
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.
High-limit switch
A high-limit switch shuts the burner off when boiler water gets hotter than it should, protecting the heat exchanger and the system from overheating.
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 →Zone valve
A zone valve lets one boiler heat several areas at different temperatures by opening or closing the water flow to each zone on demand.
What a technician checks →Circulator pump
The circulator is the pump that moves heated water from a boiler out to the radiators, baseboards or in-floor loops and back again.
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.
Every boiler part explained — what it does, how it fails and what a technician checks.
Documented for New Yorker Boiler GHE-II Combi.
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
- GHE-II High Efficiency Combi Boiler — Installation, Operating & Service Instructions (English), doc 110329-10 (11/25), Section 19 Table 19-5 · 110329-10 · accessed September 9, 2026
Facts checked September 9, 2026. Last updated September 9, 2026. Technical reviewer: not yet assigned.