170 Venturi blockage / position mismatch

What the control is telling you

The venturi position detected doesn't match the value calculated and stored in the PC Board memory.

Applies to: I-Series Plus boilers — 150K BTU and smaller and 175K BTU and higher (Combi and Solo)

Likely causes

• Obstructed intake, exhaust chamber or vent termination
• Debris build-up in the venturi
• Clogged condensate trap
• Venturi needs reset after service
• Faulty gas valve/venturi assembly

Test and repair steps

1. Check the whole vent system—intake, exhaust chamber and terminations—for obstructions.
2. Remove the gas valve and venturi assembly from the fan motor and inspect/clean debris from the venturi.
3. Make sure the condensate trap isn't clogged; resetting with a clogged trap will bring code 170 back.
4. Reinstall the venturi and call for heat; if the code returns, continue.
5. Reset the venturi hold SW2 and SW3 together until 'P' shows, then hold both again until 'PCL' appears; the unit should resume normal operation.
6. If the reset doesn't clear code 170, replace the gas valve and venturi assembly.