Boiler Cleaning and Preventative Trouble-Shooting: Now is the Time.

By: Peter Kirtschej, Service Advisor, ABR Wholesalers, Inc.

MI Peerless Boiler

To ensure optimal operation, it is important that all boilers – whether high efficiency or standard efficiency – should be cleaned before the start of each heating season. Not sure where to begin?  Follow the steps below for my tried and true method.


  1. To start, fire the boiler – watch and listen to the ignition to make sure that there is no delayed ignition.
  2. Look at the water pressure of the boiler – it should be at or close to 12 psi (It is not uncommon to see pressure between 12 and 15 psi).  
    • If the water pressure is higher than 15 psi, adjust the fast fill valve to see if it will bring down the pressure to 12-15psi.
    • If this adjustment does not change the water pressure, the fast fill valve may need to be replaced.
  3. If the expansion tank is water logged, it has failed and needs to be replaced.  Why? Internal water pressure inside the boiler has nowhere to go but out now.
    • Expansion tanks are used in closed loop systems because we cannot compress water.  When the water temperature in the heating system rises, the water expands. Inside the expansion tank is a bladder.  As the system pressure rises, it expands.  On the other side of the bladder is a cushion of air.  As mentioned above, that air pressure should be 12 psi on most residential systems.
  4. The air pressure on the bottom of the tank can be checked with a tire pressure gauge.  Note: Every time the air is checked, a little air escapes.  Air can be added back into the tank with a bicycle tire pump.
  5. Check the circulator pumps to make sure they are running; check the flanges to make sure they are not leaking.
    • Look at the placement of the circulator pump. The expansion tank always needs to be on the suction side of the circulator pump.  This is referred to as pumping away.  If you pump toward the expansion tank, pressure will decrease at the system’s highest point.  Air bubbles will expand and gather together, which may create noise during operation.
  6. After checking the expansion tank, look at the automatic air vent. 
    • The air vent usually sits on top of the air scoop with the expansion tank mounted below.  As air makes its way through the system, the air scoop lets air to the top, then the float inside the automatic air vent lets the air out of the system.  These floats get water logged, or build up with sediment, and when they do they need to be cleaned or replaced.
  7. Visually inspect the whole system, including piping, venting, and electrical.


  1. Wearing a good respirator and gloves, turn off the boiler and pull the burner assembly.
  2. Clean out the burners (I prefer to use a wire brush).
  3. If working on a high-efficiency boiler, pull the front plate of the heat exchanger and clean the burner basket with a soft brush.
  4. On boilers that are really dirty, sometimes a vacuum is not enough for the basket.  In this case, washing the basket with water is necessary.  If water is used, don’t forget to blow out the water from the burner bas with nitrogen or compressed air – otherwise there may be a delayed ignition.
  5. Clean the flame sensor and spark igniter with steel wool.  After cleaning, wipe down the rods with a rag or cloth.  If this is not done, the residue will create a coating once heat is applied, rendering the flame sensor and igniter dirty.
  6. On standard efficiency boilers, pull the flue – and if possible the draft hood – apart.
  7. Brush and vacuum out the pipes and the draft hood, inspecting the pipes for corrosion and brittleness.
  8. Brush the heat exchanger.  On boilers that have a section-type heat exchanger, use a long and narrow brush to get in between the sections.  Brush all the soot and dirt off, and follow with a good vacuum.
  9. Now that the exchanger is clean, inspect it with a light and mirror to see if there are any leaks.  When cleaning a high-efficiency boiler, scrub between the tubes of the exchanger with a soft brush – something the thickness of a credit card should fit perfectly.  Some exchangers require a descaler – such as Lime Away or vinegar.
  10. Rinse and drain all the residue – make sure to remove all water.  If you are cleaning a copper fine tube boiler, make sure to break down the boiler until you see the top of the exchanger, then clean out between the fin tubes.  This process takes a bit more time, but is crucial for proper heat transfer and boiler longevity.
  11. High efficiency boilers condense – due to this condensation, they require a drain and trap.  Blow out all the drain tubes, pull the trap if possible, and flush it out.  If the system has drain neutralizers, replace them as needed per manufacturer recommendations.
  12. Reassemble the boiler.

After cleaning and troubleshooting, discuss any recommendations with the home owner.  For more information, or for additional service tips, check out our website: