Plate heat exchanger (PHE) cleaning

What is going on

Removing and cleaning the domestic plate heat exchanger to remove calcium buildup. Clean regularly if the domestic water is not treated.

Likely causes

• Calcium buildup and narrowed passages from untreated domestic water

Check in this order

1. Call for heat off, let the post-purge finish, turn gas off and remove power.
2. Isolate and drain both the central heat loop and the domestic side.
3. Swing the control panel out. Disconnect the fan, gas valve, ignition and ionization electrode cabling. Disconnect the gas supply pipe at the gas valve inlet union and discard the fiber washers.
4. Once the chamber has cooled, remove the four nuts holding the burner assembly. Lift out the assembly and protect the refractory disc. Replace the refractory if damaged.
5. Remove the two flanged front screws on the CHB with a 4 mm or 5/32 in Allen wrench, holding the PHE in place. Lift the PHE out without getting water on components.
6. Check the four PHE sealing gaskets for wear and replace as needed.
7. Clean the PHE with a suitable commercial descaler or vinegar.
8. Flush the PHE thoroughly with clean water.
9. Fit new gaskets.
10. Reinstall the PHE behind the CHB and tighten the two screws.
11. Reassemble in reverse order using new fiber washers on the gas pipe.
12. Return water pressure and purge all air from the central heat side.
13. Open the domestic outlet drain or a nearby hot tap and flush the PHE for 1 minute.
14. Close the water flow and power on the boiler.

More boiler guides

• 0-10 VDC input to modulate firing rate (Mode 5)
• Annual maintenance and inspection
• Blank display
• Boiler pressure keeps dropping / FILL shows
• Boiler shows FILL and will not fire
• Cleaning the combustion side of the heat exchanger