Slant/Fin Lockout or Hold 81 — Delta T Limit (or Appliance Making Banging/hissing Sounds)
Lockout or Hold 81
Delta T limit (or appliance making banging/hissing sounds). Possible cause: insufficient water flow. Corrective actions: check Fuse B; check appliance pump; ensure plumbing is correct (Section 10.0 System Piping) and water pressure is at least 15 PSI; boiler heat transfer surfaces may be fouled with scale or magnetite — clean with Fernox DS-40 Descaler and Cleanser. The table classifies it as Lockout/Hold.
Applies to
This low-water or pressure protection code is displayed by the CHS control (Sola) on CHS models (CHS-85 through CHS-399), as documented in Slant/Fin CHS 85-399 Installation and Operation Manual, 84703 (V.2018-07-11) (84703). Codes can differ between controller generations, so always check the manual that matches your unit.
- Slant/Fin CHS Series (CHS-85 to CHS-399)
- Slant/Fin CHS-85
- Slant/Fin CHS-110
- Slant/Fin CHS-154
- Slant/Fin CHS-175
- Slant/Fin CHS-201
- Slant/Fin CHS-285
- Slant/Fin CHS-340
- Slant/Fin CHS-399
Controller: CHS control (Sola). Source manual: 84703.
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.
Magnetic dirt separator
A magnetic dirt separator removes iron oxide sludge and other debris from heating water before it can coat the heat exchanger.
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 Slant/Fin CHS Series (CHS-85 to CHS-399).
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
- Slant/Fin CHS 85-399 Installation and Operation Manual, 84703 (V.2018-07-11) · 84703 · accessed September 9, 2026
Facts checked September 9, 2026. Last updated September 9, 2026. Technical reviewer: not yet assigned.