Lochinvar Crest Delta T Shutdown — Temperature Rise Across the Heat Exchanger Exceeded the Set Parameters
Delta T Shutdown
Temperature rise across the heat exchanger exceeded the set parameters. The temperature rise across the heat exchanger has exceeded the set parameters for the boiler, so verify the system is full of water and all air has been purged, verify the boiler is piped properly, check for voltage to the boiler pump motor on a call for heat, replace the pump relay if necessary, and verify the boiler pump is set to the proper speed or is the proper size.
Applies to
This fault code is displayed by the Crest control (text faults) on Crest with Hellcat models (FCB1000 through FCB6000), as documented in Crest with Hellcat (FCB) Service Manual, 100343237 Rev D — Table 3G fault codes (100343237 Rev D). Codes can differ between controller generations, so always check the manual that matches your unit.
- Lochinvar Crest (FB / Hellcat FCB)
- Lochinvar Crest FBN0751
- Lochinvar Crest FBN1001
- Lochinvar Crest FBN1251
- Lochinvar Crest FBN1501
- Lochinvar Crest FBN1751
- Lochinvar Crest FBN2001
- Lochinvar Crest FBN2501
- Lochinvar Crest FBN3001
- Lochinvar Crest FBN3501
- Lochinvar Crest FBN4001
- Lochinvar Crest FBN5001
- Lochinvar Crest FBN6001
- Lochinvar Crest FCB1000
- Lochinvar Crest FCB1500
- Lochinvar Crest FCB2000
- Lochinvar Crest FCB2500
- Lochinvar Crest FCB3000
- Lochinvar Crest FCB4000
- Lochinvar Crest FCB5000
- Lochinvar Crest FCB6000
Controller: Crest control (text faults). Source manual: 100343237 Rev D (2025-07).
Why a code is not a diagnosis
The code reports the condition the control detected; the underlying cause must be confirmed on site by a licensed technician using the manufacturer's procedure.
Safe things to observe
- Note the exact code, when it appears and what the appliance was doing.
- If the appliance has stopped, call a technician rather than repeatedly restarting it.
- If you smell gas, stop, go outside and call your gas utility's emergency line or 911 before anything else.
Do not
- Do not ignore a code that returns after a reset.
How professional service helps
- A licensed technician diagnoses the cause with the manufacturer's test procedure.
- 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.
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 →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…
- 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 Lochinvar Crest (FB / Hellcat FCB).
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
- Crest with Hellcat (FCB) Service Manual, 100343237 Rev D — Table 3G fault codes · 100343237 Rev D · accessed September 7, 2026
Facts checked September 7, 2026. Last updated September 7, 2026. Technical reviewer: not yet assigned.