NTI Trinity TFT 51 — Illegal Modbus Write Was Attempted
51
Illegal Modbus write was attempted. The control recorded this alert for Illegal Modbus write was attempted, and alert code 51 is listed in Table 16-4 Alert Codes. The table classifies it as Alert.
Applies to
This communication or network fault code is displayed by the TFT control (Honeywell SOLA) on TFT models (TFT60, TFT85, TFT110, TFT154, TFT201, TFT285, TFT340, TFT399), as documented in Trinity TFT60-399 Installation and Operation Manual, doc 99984535 (2024-04-08), sections 16.1–16.3 (99984535). Codes can differ between controller generations, so always check the manual that matches your unit.
- NTI Boilers Trinity TFT (discontinued)
- NTI Trinity TFT60
- NTI Trinity TFT85
- NTI Trinity TFT110
- NTI Trinity TFT154
- NTI Trinity TFT201
- NTI Trinity TFT285
- NTI Trinity TFT340
- NTI Trinity TFT399
Controller: TFT control (Honeywell SOLA). Source manual: 99984535 (2024-04-08).
Why a code is not a diagnosis
A communication code involves the link between controls (cascade, remote, sensors on a bus). Another unit being off, a wiring fault or an address conflict can all produce it.
Safe things to observe
- Check that every appliance in a multi-unit plant has power.
- Report the code together with any other codes on the system.
Do not
- Do not re-address or rewire control networks yourself.
How professional service helps
- A technician verifies power, wiring and settings across the connected units.
- 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.
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
- Trinity TFT60-399 Installation and Operation Manual, doc 99984535 (2024-04-08), sections 16.1–16.3 · 99984535 · accessed September 7, 2026
Facts checked September 7, 2026. Last updated September 7, 2026. Technical reviewer: not yet assigned.