Clean the DHW filter (combi models only)

What is going on

If you have a combi and the hot water has gone weak or lukewarm, or the boiler will not see the flow, the first thing to look at is the DHW inlet filter and the flow meter turbine. They collect grit and scale, especially on new plumbing or after the city does work on the main. Cleaning them is a simple job, but the domestic side has to be valved off and drained first so you are not working under pressure. It takes about twenty minutes and often fixes the complaint outright.

Likely causes

• Debris or scale clogging the DHW inlet filter
• Grit jammed in the flow meter turbine so it spins slowly or not at all
• Recent plumbing work or water main disturbance sending sediment into the combi
• Hard water scale building up on the turbine over time

Check in this order

1. Valve off and drain the combi DHW circuit before starting.
2. Remove the clip on the flow meter, then remove the flow meter cap.
3. Remove the flow meter turbine and check that it spins freely by hand.
4. Remove the filter and clean it with a toothbrush and clean running water.
5. Reinstall the filter, turbine and cap, making sure everything seats fully.
6. Refill the DHW circuit and purge it following the filling and purging instructions.
7. Restore gas and power, check for leaks at the work area, and run a hot water draw to confirm flow is back.

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