The boiler is different form the furnace. Boiler has two parts, furnace part and hydronic part. For the boiler troubleshooting we should have having a good understanding of the system.

A boiler does not have a blower motor to force the air to the house but has a hydronic pump. The furnace part is the same as the troubleshooting as the furnace with some differences that we point them out in below. For the boiler troubleshooting,  We assume that boiler installed by code with a good performance of years. Now the boiler is not working properly. First, we do a Call for heat!

Boiler does not start up

  1. Check the thermostat, if it is a battery operated, double check whether the battery is full or not. If the thermostat operated based is on mercury contact, see if the correct contact is made.
  2. Check the power line, if 120 volt comes to the boiler. Double check the power switch.
  3. Check the fuses, if replace need it.
  4. Check the water level, if the water level is low, the Low Water Cut off (LWC) turns the boiler off. Add water to the boiler and check the reasons why the water level is low.
  5. Faulty LWC needs to be replaced.

Vent Motor does not start

  1. Measure the voltage to the vent motor, whether you get 120V or not. If not replace the control board.
  2. If you do not have 120V from the control board still need to check the vent motor too. Give a power of 120 volt externally to see weather the vent motor start or not, if it is starting, great. If not, the vent motor need to be replace as well.

Boiler starts and the vent motor turns on but no heat at the house

  1. Check the pressure switch is closing or not. Measure the air pressure of the pressure switch if it does not match the pressure on the pressure switch, then replace it.
  2. Check the igniter, if igniter turns on or not, if not, check if the igniter receives 120 volts. If there is a 120 volt, replace the igniter.
  3. If the igniter not receiving 120 volts, then power the igniter externally, if it turns on, then replace the control board, if not then the control board and igniter need to be replaced.
  4. If igniter turns on but not hearing the click of the gas valve. Check the power to the gas valve, if there is a 24 volt, replace the gas valve. If not 24 volts to the gas valve, replace the control board.

Boiler starts up, the burner turns on and the boiler is functioning but no heat, yet

  1. Check the pump, whether the supply pump or circulate pump is working properly. If the pipe is hot right after the supply pump or not. If the pump is getting hot itself but the pipe after the pump is not hot, replace the pump.
  2. If the pipe after the pump gets hot, but the returns water is not hot, check the zone valves and the air in the system.
  3. Check if the zone valves are opening, if it is not opening, check if 24 volt goes to the zone valves but not opening, replace the zone valve.
  4. If 24 volt is not going to the zone valve, check the transformer, the bad transformer needs to be replaced.
  5. If the transformer is proper, check the relay, module or control board

Air Lock

The most common problem is air in the system

  1. There are few air vents installed in the hydronic system. A lot of times they are not working properly, manually open it and let the air out.
  2. If there are radiators or baseboards, check the air vents over there and let the air out.
  3. If the air couldn’t be out with the help of the air vents, it needs to be drained.
  4. Draining the boiler is a procedure. Find the shut-off valve and the drain valve on the return pipe. Close the shut-off valve, connect a hose to the drain valve. If the system is not a closed system and is hooked up to the city water, then open the drain valve start drain until all the air comes out.
  5. If the boiler is a closed system, the supply pipe needs to be connected to the city water and run the drain.
  6. Note: paying attention needs it for the cross connection when connecting to the city water of the boiler system. If the boiler has no glycol, a check valve needs to have on the line; otherwise, a Reducer Pressure Principle (RP) as a Backflow preventer must be installed first then a drain connection to connect the city water line.
  7. Shut the shut-off valve on the return pipe, open the draining valve on the returning pipe while the supply line has been connecting it and running it. This procedure should run till no air can be found on the draining.
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