Boiler Repair

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Fan Repair

  • Year Repaired: 2020 – Present
  • Symptoms: F9 error – Blower speed too low at burner start.
  • Cause: Boiler had a flue gas leak, condensate hose was backed up, and the exhaust return flapper was worn. All of this was putting dirty exhaust back into system and clogging fan bearings.
  • Outcome: Radial fan was replaced
  • Material Cost: $950
  • Time: 3 hours (after diagnosis)


Radial Fan Replacement Manual


The full system was inspected and had a lot of dirt retained in the system. The system was vacuumed, and the condensate p-trap was cleaned. The flue gas gasket was re-sealed with gorilla glue. The air-gas venturi was vacuumed and air was blown in to release trapped dirt. Initially the fan bearings were cleaned and oiled and the fan was working but soon it clogged up again and would not spin freely. Once the fan was replaced there were no issues. The exhaust return flapper was also replaced.

Air Pressure Switch

  • Year Repaired: 2021 – Present
  • Symptoms: F5 error – faulty air pressure switch. Blower starts up but no ignition after 51 seconds.
  • Cause: Faulty sensor
  • Outcome: Replaced air pressure switch
  • Material Cost: $100
  • Time: 1 hour (after diagnosis)


While waiting for the air pressure sensor to come in, the leads on the sensor were checked and were very oxidized. They were wire brushed and the wiring female spade connectors were replaced. The sensor error was very intermittent and could not be replicated in person, but since the sensor replacement fixed the issue, it can be concluded this was the issue.

More things that were tested were the air-gas venturi ports and the rubber vacuum tube connected to the switch. The air switch was also opened up and no visible issues were present. The condensate hose drainage was tested with no issues. The flue gas exhaust was tested with no leaks pointing to no issues with the vacuum pressure.

Flame Sensor

  • Year Repaired: 2021 – Present
  • Symptoms: F4 error – no flame signal present. Repetitive clicking signalling sparking but no flame sensed.
  • Cause: Oxidized flame sensor
  • Outcome: Sanded flame sensor
  • Material Cost: $30
  • Time: 1 hour (after diagnosis)


Since the flame sensor oxidizing is a common problem, it was the first thing I inspected. It ended up being very oxidized so I scraped it off until it was clean.

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