System water fill, purge and test

What is going on

Fill and purge on the TRX150. Do it at install and after any service that opens the loop. Air in the system means noise, no flow, cold rads, pump cavitation. Condensate line goes on first so nothing gets wet when you fire it later. Purge zone by zone, then DHW.

Likely causes

• New install with a dry heat exchanger and piping
• System drained for service or a part swap
• Air trapped in a high point or a zone with no vent
• Pressure dropped after a leak or weeping fitting
• Combi DHW side not flushed after install

Check in this order

1. Connect the condensate discharge pipe before filling and purging the heating circuit.
2. Open the main water valve slowly until water flows. Do not open it fully.
3. Purge each zone starting at the lowest point, closing it only when clear water with no air shows.
4. Use the automatic air purge valve in the boiler and open the manual air vent if fitted.
5. Keep filling until at least 12 psi shows on the pressure gauge.
6. Watch that the boiler holds 12 to 15 psi during the purge, since pressure sags as air leaves.
7. Purge DHW by opening faucets nearest the boiler first, then the farther ones, until water runs freely.
8. Recheck the pressure gauge after a cycle or two and top up if it dropped.

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