Patterson-Kelley · Error codes
Patterson-Kelley 10205 — Maximum Stack Temperature Reached
10205
Maximum Stack Temperature reached. The Cascade Master is setup to use a bypass valve. No boiler in the cascade system has a bypass valve selected as a relay assignment. On the boiler that the bypass valve is connected to, change one of the assigned relays to be a bypass valve. If a bypass valve is not used then change the Cascade Master - Valve Control -Use Bypass The table classifies it as Hold (H).
Applies to
This domestic hot water fault code is displayed by the NURO touchscreen control with Sola burner control on MODU-FIRE FD (N750–N3000) and THERMIFIC VELOX (N750–N2000) appliances equipped with the NURO touchscreen control, as documented in NURO Advanced User's Guide, doc 1004905979 Rev G (March 2016), Appendix C Error Reference Table (1004905979 Rev G). Codes can differ between controller generations, so always check the manual that matches your unit.
- Patterson-Kelley P-K MODU-FIRE FD
- Patterson-Kelley P-K THERMIFIC VELOX
- P-K MODU-FIRE FD N750
- P-K MODU-FIRE FD N1000
- P-K MODU-FIRE FD N1500
- P-K MODU-FIRE FD N2000
- P-K MODU-FIRE FD N2500
- P-K MODU-FIRE FD N3000
- P-K THERMIFIC VELOX N750
- P-K THERMIFIC VELOX N1000
- P-K THERMIFIC VELOX N1500
- P-K THERMIFIC VELOX N1700
- P-K THERMIFIC VELOX N2000
Controller: NURO touchscreen control with Sola burner control. Source manual: 1004905979 Rev G (2016-03).
Why a code is not a diagnosis
A DHW code involves the hot-water side: sensors, flow, the mixing/bypass valve or the DHW heat exchanger. It does not say whether the fix is a sensor, a valve or a flush.
Safe things to observe
- Note the code and whether the problem follows a hot-water draw or appears at all times.
Do not
- Do not open the appliance to test DHW components yourself.
How professional service helps
- A technician tests the DHW sensors, flow switch and valve circuits, and cleans the DHW path where the manual directs.
- 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.
Flue temperature sensor
The flue temperature sensor — sometimes called the stack or exhaust sensor — measures how hot the gases leaving the boiler are.
What a technician checks →Differential-pressure bypass valve
A differential-pressure bypass valve opens when system pressure rises — usually because zone valves have closed — so the boiler keeps enough flow to…
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…
Every boiler part explained — what it does, how it fails and what a technician checks.
Documented for Patterson-Kelley P-K MODU-FIRE FD and Patterson-Kelley P-K THERMIFIC VELOX.
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
- NURO Advanced User's Guide, doc 1004905979 Rev G (March 2016), Appendix C Error Reference Table · 1004905979 Rev G · accessed September 9, 2026
Facts checked September 9, 2026. Last updated September 9, 2026. Technical reviewer: not yet assigned.