Overview
Two green flashes on Baxi 816/825/830 Heat models indicate a "shutdown input" fault. The boiler has detected an open circuit on the BL terminals of the User Interaction Controller (the board that accepts a volt-free external safety/shutdown signal). Those BL terminals are used for external devices or links (for example a condensate pump float switch or an interlock). If the BL circuit is open the boiler will shut down as a protective measure and display the 2-flash code. This is a protective, non-urgent safety shutdown but it will prevent the boiler from supplying heat or hot water until the input circuit is restored. The cause can be simple (a missing or broken link, a disconnected or failed condensate pump or float switch, blocked/frozen condensate drain) or electrical (wiring fault, connector fault, or a controller/PCB fault). Some basic checks are reasonable for a competent homeowner, but anything involving internal wiring, PCB testing, or gas/electrical isolation should be performed by a Gas Safe registered engineer.
Possible Cause: BL terminals on User Interaction Controller are open circuit
Troubleshooting Steps
Safety first
- If you smell gas or suspect a gas leak, leave the property immediately and call the gas emergency service. Do not attempt any checks.
- Before opening the boiler cover or touching wiring, switch the boiler off at the isolator and turn off mains power at the consumer unit. If you are not confident working with mains electricity or boiler internals, stop and call a Gas Safe engineer.
- Do not try to permanently bridge or bypass safety terminals to force the boiler to run.
Initial homeowner checks (safe, simple checks)
1. Reset the boiler once: follow the manufacturer reset procedure (hold the reset/select for ~5–10 seconds). If the code clears and stays cleared, monitor for recurrence. If it returns immediately, continue diagnostics.
2. Check whether a condensate pump is fitted and connected to the boiler. Locate the pump (usually near the condensate trap or upstairs in an airing cupboard). Is it powered? Is the power LED on? Does the pump run if you pour a small amount of water into its collection tray (this will test float and motor)?
3. Inspect external condensate pipework for blockages, kinks, or freezing (particularly in cold weather). Thaw frozen pipes with warm water (not boiling) and clear any debris. Ensure condensate trap and pipe are free-flowing.
4. Visually inspect the boiler front/user interaction edge for any obvious loose external wiring or damaged connectors; do not remove internal covers unless competent.
Specific diagnostic and fix steps (for competent DIYers only)
1. Locate the User Interaction Controller/BL terminals (refer to your boiler manual for exact location). If you are uncertain, do not proceed — call a pro.
2. With the boiler mains isolated, check for a removable link across the BL terminals. Some installation types require a link if no external safety device is fitted. If the link is missing and no external device should be fitted, replace the link exactly as the manual specifies. Do not improvise.
3. If a condensate pump or other device is fitted to BL, check the wiring connections are secure at the BL terminals and at the pump. Re-seat any loose connectors. With power off, check for broken/frayed wires and repair with appropriate connectors.
4. If you have a multimeter and are competent: with power off, check continuity across the BL terminals where they should be closed when the external device is satisfied (or closed by the link). Restore power only if you understand live testing procedures. If the BL remains open with no external device, the controller or its connectors may be faulty.
5. If the condensate pump is not running but has power to it, check its float switch and motor. Replace or repair the pump if faulty. If the pump is running but the BL input still reads open, the wiring between pump and BL or the pump’s voltage-free contact may be faulty.
When to call a professional
- If any step requires you to open the boiler casing, test live circuits, repair PCB wiring, or work on gas components, stop and call a Gas Safe registered engineer.
- Call a professional if: the BL terminals show open circuit after the obvious checks; you cannot locate/replace a missing link safely; the condensate pump is working but the boiler still faults; the fault recurs after resets; or you are unsure of any step.
What information to give the engineer
- Model and serial number of the boiler, the exact displayed error (2 green flashes / shutdown input), whether a condensate pump is fitted and what you tested (pump runs/doesn't run, condensate drains clear/blocked), and any wiring or link observations.
Final notes
- Do not repeatedly reset the boiler if the fault returns — this can mask the real fault and risk further issues. The BL input is a safety feature; do not bypass it. If simple homeowner checks do not resolve the issue, arrange for a Gas Safe qualified engineer to diagnose and repair the wiring, external device or controller/PCB as required.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi 816 Heat, 825 Heat, 830 Heat.