Replace the fan and mixer

What is going on

The fan and mixer on the TRX150 come off as one assembly, and that is how I usually do it. The thing that bites people is the fuel setup. The gas diaphragm and mixer are different for natural gas and propane, and a mismatch gives you bad combustion, rough starts or a lockout. Most fan jobs go wrong at reassembly, either a pinched O-ring or a missing gasket, which leaks and throws the combustion off.

Likely causes

• Failed fan or noisy bearings after years of running
• Fan not reaching speed, giving blocked or low airflow errors
• Damaged mixer O-ring leaking air or gas
• Wrong gas diaphragm or mixer for the fuel type after a swap

Check in this order

1. Turn off power and shut the gas supply before starting.
2. Remove the silencer and gas line.
3. Loosen the three screws holding the mixer to the fan. Check the O-ring is not damaged and replace it if it is.
4. Loosen the three screws holding the fan to the heat exchanger.
5. Reassemble the mixer and fan in reverse order with the O-ring between them.
6. Reinstall the fan and combustion assembly and fit the gasket between the fan and air inlet channel.
7. Confirm the gas diaphragm and mixer match the fuel (natural gas or propane).
8. Leak-check the gas connection, then verify combustion with an analyzer. Gas work is for a licensed technician.

More boiler guides

• Access the low voltage wiring connections
• Blocking errors versus lockout errors
• Blower not running
• Blower runs at high speed with burner off
• Boiler bangs or hisses; Lockout 81 delta T
• Burner not running on a call for heat