Boiler Circulation Problems - Components for a Boiler Circulator Pump

This pump has a coupling device between the motor and the impeller.

Boiler Circulation Problems | Troubleshooting Hydronic Water Loops – Richard, we have a hot water boiler and we are having problems with the circulation of the water. The radiators are cool and we don’t seem to have good heat. The boiler seems to be working fine but the radiators are cool. Can you give me some insight into my boiler circulation problem? Kate

Boiler Circulation Problems | Troubleshooting Hydronic Water Loops

Kate, there can be several things wrong that keep the water from circulating through the water loop. The first place to start is the circulator pump. This should be located near the boiler in the near boiler piping. I would check the aquastat to make sure it is engaging the circulator pump as the aquastat has a relay that turns the circulator on when there is a call for heat and the temperature inside the jacket is the right set point temperature according to what the aquastat is set for in temperature ranges.

The best way to do this is with a multi-meter to make sure the output to the pump is 120 volts. Most pumps for residential systems work off of 120 volts. If you have 120 volts on the terminal connections where the wires go to the pump then the aquastat is good and the relay is working as it should.

Now you should check the pump. You want to know if there is flow going through the pipe from one side of the pump to the other. As always, when dealing with electricity always use basic electrical safety procedures. Electricity is dangerous especially for someone who knows nothing about it. When in doubt, call a professional.

Boiler Circulation Problems | Troubleshooting Hydronic Water Loops

Some pumps have a linkage or coupling device. This device connects the motor to the bearing assembly where the impeller is located. The impeller pushes the water through the pipe and some pumps do not have coupling devices but are direct drive. In other words, the pump motor is directly attached to the impeller with certain pumps. Pumps with coupling devices need to have the coupling device inspected to make sure it is not broken. If the coupling device is broken it needs to be replaced and that was your circulation problem.

If it is a direct-drive circulator pump then you need to inspect the impeller to make sure it is good. Impellers do go bad from time to time and need to be replaced.  If this is the case, you should really call a boiler technician to fix the problem.

Furthermore, many will have the parts on their truck and can have you up and running in an hour or so. They will also know the correct procedure for replacing the impeller without causing additional problems which if you really do not know what you are doing you can cause additional problems. Other problems with the circulator can be a bad motor or a leaking bearing assembly. Some circulator pumps require maintenance while other pumps are maintenance-free.

Boiler Circulation Problems - Air Problems and Troubleshooting

Automatic Air Vent Water - Air Bleeders for Hydronic loops

Automatic Air Vent or Automatic Air Bleeder

The next thing that can cause the water not to circulate in the water loop including to the radiators is a hydronic airlock. This is when you get air into the loop. Air will build up usually on a riser or in a radiator. It is necessary to remove the air from the system. Many radiators and even baseboards have manual air bleeders on them. The air bleeders require a key to open them and hopefully, you have an air bleeder key.

If you have an air bleeder key then you can go around to all your radiators and open these air bleeders with the key. Furthermore, air management in your boiler loop systems is important.  Finally, it could also cause boiler pressure problems causing your pressure relief valve to vent.

Take a rag with you and open the air bleeder until you get water. In some cases, you will get water only and in other cases, you will get lots of air. Let all the air bleed from the system. As much as possible. Your system should also have automatic air bleeders or automatic air vents located somewhere in the loop. Typically these are located on the risers of the piping.

Furthermore, they automatically vent any air that gets into the loop. They are usually very reliable and need little maintenance. However, from time to time they can stop working and need to be replaced. Again if these need to be replaced an HVAC technician should replace these.

Boiler Circulation Problems | Troubleshooting Hydronic Water Loops | Conclusion

One last thing you can check if you have circulation problems is the shutoff valves in the piping. If someone haphazardly played around with one of these valves and turned it off then you will definitely not have the flow going through the water loop. Check to make sure these valves are open. Hopefully, it is as simple as opening a valve but probably not the case. Good Luck to you and I hope your problem gets solved soon.

Boiler Circulation Problems - Troubleshooting Hydronic Water Loops

Boiler Circulation Problems | Troubleshooting Hydronic Water Loops

See our other helpful HVAC calculators placed throughout the site:

Use our handy calculator to see how many BTU's your natural gas appliances are producing: