Have you noticed a decrease in the amount of heat produced by your boiler and/or radiators? If you have, it could be due to a faulty circulator pump, which is responsible for circulating the hot water from your boiler to your radiators and back to your boiler. Thankfully, there are some things you can check to determine if is it your circulator pump and if you need to call a professional.

Since a circulator pump is a moving part with rotors, bearings and impellers, it can fail or malfunction if one of those parts becomes excessively worn or damaged. The good news is that the circulator pump often gives off warning signs before it completely stops. If you are using an intelligent high efficiency pump, it would be much easier to inspect the pump faulty, as the circulator pump itself can show you the fault code meaning the likely causes to the pump faulty.

1. Your Circulator Pump Fails to Turn On.

When your circulator pump is not on, it could mean that the pump has completely failed, the aquastat is not functioning, no power is reaching the pump or the boiler is failing to heat the water. The first thing to check is if the water pump is on or functioning. Modern water pumps tend to be extremely quiet, but if it is running, you should be able to hear it. If you can’t hear it, the pump is most likely not operating. To test this theory, you can carefully touch the pipes around the circulator pump. If they’re cold or only slightly warm, the hot water is not circulating.

There could be many causes for your circulator pump failure, such as the circulator pump has failed or the lack of water circulation is due to another problem, like a faulty aquastat or problems with your boiler’s heating elements, burners or heat exchanger.

If the circulator pumps has failed, the likely causes are

• Loose power cable connection. So please make sure the power cable is connected securely and firmly.
• The input voltage is too high or too low. Then just check if the voltage is within normal range.
• The pump rotor is blocked. Then you should disassemble the motor and check if the rotor can rotate normally. If not, then clean up the impurities to make the rotor part rotate flexibly. The article “How to avoid blocked circulator pump” would tell you in details how to do with it.
• The impeller and motor may be winded by fibers or jammed with sundries. Then you have to remove the impeller housing and clean them.
• One or more phases of the internal connection circuit is disconnected or short circuit of internal connection circuit. At this time, you should replace the pump with a new one.

2. The Pump Is Making Odd or Loud Noises.

If you notice your circulator pump making loud or odd noises, something could be wrong with the pump, or there could be air in the hot water lines. 

If the problem is air in the lines, the entire system will need to be drained. Any leaks will need to be repaired, and the entire system will need to be refilled. Some circulator pumps have an air bleeder screw, or you can loosen the union nut to release the air. Open the lock nut slightly until you hear air hissing, then tighten up again as water begins to leak.

If the pump is the source of the loud noises

• This often indicates that something inside the pump is failing, like a bearing, a bad valve or an improper pump installation that has resulted in the pump not being precisely aligned with the pipes. The only way to accurately diagnose this type of pump problem is to remove the pump and examine all the valves, seals and moving parts for defects and wear and tear.

• Calcium or lime deposits can also built up and create noise that makes a ‘hush pump’, not so quiet. The impeller housing of a circulator pump can be removed to inspect the impeller. Be sure to cut off power first, and close valves on each side of the pump. Inspect the impeller surfaces for any deposits. They can be removed with a stiff brush, or a chemical like CLR.

• If the water flow rate is too high, it could also make a noise. At this time, reducing the suction head of the pump would be helpful.

• In the heating system, the system pressure is stable. But if the pump inlet pressure is too low, the noise would occur. To solve the problem, you could increase the inlet pressure, or make sure that the air volume in the expansion tank is sufficient, if installed.

3. You Can See the Pump Leaking.

Over time, the mounting bolts can corrode and break, and the valves and seals can wear out. When this happens, water can leak from the pump, causing it to not operate as efficiently or at all, depending on how much water is leaking. When this happens, the valves, seals and mounting bolts will need to be replaced in order to stop the leaks.

4. You Have a Dramatic Loss of Heat at Your Radiators.

If your radiators are not producing heat or are producing very little heat, it could be a problem with the water circulation to and from your boiler, which means the pump has failed or the pump performance is too low. Then you could increase the suction head of the pump by setting the pump to a higher speed or higher constant pressure.

When the pump isn’t circulating hot water, your boiler and radiators become dramatically less efficient. This is because the only thing circulating the water through your system is heat convection, which can be extremely slow. Due to this inefficiency, you may notice your heating bills increase while the overall temperature of your building decreases.

If you have a multi-zone boiler system that contains several circulator pumps, you may only notice that some of your radiators are not producing heat. When only a few radiators are affected, it means that at least one of your water pumps has failed or need to increase the suction head.