Multiple zone valve installation (C) Daniel FriedmanChecks for Circulator Pump & Circulator Relay Operation

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Here we explain simple procedures for determining whether the circulator pump is working on a heating system. This article series discusses Circulator Pumps: how to find, inspect, diagnose, and repair problems with Hot Water Heating System Circulator Pumps or circulator pump relay switches and controls.

This article series answers most questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs.

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How to tell if the circulator pump is working - some circulators are quiet - which pipes to feel

Older model B&G Red Circulator Pump (C) Daniel FriedmanHot Water Heating System Circulator Troubleshooting & Repair Guide: we discuss circulator pumps, circulator pump relay switches & controls on heating systems to describe how to tell if a heating circulator pump is working. Some examples of questions and problems that show up first as a symptom:

Why do some heating zones work and others not?

Why does heat come out of zones where thermostats are not calling for heat?

How to fix an air-bound heating system and blocked circulator pump.

Is the circulator pump running? If the motor runs that doesn't mean that the pump is actually moving hot water through the system.

Article contents

First Things to Check in Diagnosing a Bad Circulator Pump

First, before checking the circulator pump for proper operation, we need to be sure that the heating system controls are calling for heat:

1. The heating boiler must be turned on and able to run

2. The thermostat must be set up to call for heat

3. In response to the thermostat you should hear the heating boiler turn on and run;

4. You can then examine the heating system distribution piping leaving and returning to the heating boiler, identify the circulator pump (or pumps if there is more than one), and feel the heating water piping at the pump(s).

5. Identify the circulator for the heat zone where you have turned up the thermostat:

Check the Operation of a Single Hot Water Heat Circulator Pump - a Single Heating Zone

If there is only one thermostat, one heating zone, and one circulator pump it's simple, there is nothing to sort out, continue with INDIVIDUAL HEAT ZONE CHECK. There will be no zone valves, just a single pump and its controls to turn the circulator pump on and off.

The heating distribution piping in a one-zone building may still be divided into multiple "branches" or sub-loops. If that is the case, you might be able to convert this system to individual zone controls by adding zone valves at the individual heating water piping loops - provided that the loops are arranged in parallel, not in series.

Check the Operation of a Multi-zone Heating System Using a Single Circulator Pump

Multiple zone valve installation (C) Daniel Friedman

Multiple thermostats, multiple heating zones, one circulator, multiple Zone Valves:

[Click to enlarge any image]

If there are multiple thermostats there may still be only one circulator (if zone valves are installed) and individual heat zones are controlled by motorized zone valves that open or close to let heating water flow through that heating pipe loop.

In that case the same procedure as below for "feeling the circulator piping" is used but you feel the piping at the zone valve as well - since if a zone valve is not opening no hot water will flow.

Our photo (left) shows a 6-zone hot water heating system using six individual zone control valves and a single circulator pump.

See ZONE VALVES, HEATING for details about how these devices work and how they are inspected and repaired.

Check the Operation of a Multi-zone Heating System Using Multiple CIrculator Pumps

Multiple circulator pumps and zones (C) Daniel Friedman

Some buildings use one circulator pump (and controlling circulator relay switch) to control each individual heating zone (instead of "zone valves" as above).

In this case if you don't know which circulator pump and pipe loop supplies the zone for which you turned up the thermostat, just go to INDIVIDUAL HEAT ZONE CHECK just below, but feel the piping at each circulator pump.

Our photo (left) shows an 8-zone hot water heating system using eight individual Bell & Gossett™ circulator pumps. Notice those rust marks at the bottom pump flange at some of these units?

All eight pumps had been installed in the previous two years - at a previous inspection we found the predecessor pumps leaking so badly that the floor of the boiler room was puddled with heating water. The installer needs to inspect, clean, and re-make the leaky connections on these new circulator pumps to avoid a repetition of the same problem.

Individual Heating Zone Operation Checks

How to know if a particular hot water heating zone is working or calling for heat:

Listen to the circulator pump: is it running? Bell & Gossett circulators are generally audible, making some electrical motor noise. Grundfoss circulator pumps are quieter but should be audible. Taco circulator pumps are often so quiet that you cannot rely on sound (or I can't), but it's easy to go on to the next step: feeling piping temperatures.

Incidentally if a heating zone circulator pump is very noisy or has become more noisy than when it was installed, there may be a problem with a failing motor bearing, pump assembly bearing, or pump impeller.

Feel the Hot Water Heat Piping at the Circulator Pump: You can feel the pipe at the circulator pump - doesn't matter which side - in or out flow - since if the pump is running the pipe will get warm, then hot.

If the circulator is on the pipes that are LEAVING the boiler and sending heat into the building (not the best location) it's better to feel the pipe on the outlet side of the circulator since the pipe at the inlet side might be hot just by convection heat rising from the boiler.

If the circulator pump is on the RETURN side of the heating piping loop (the usual and better location) then you can feel the pipe at the circulator pump - doesn't matter which side - in or out flow - since if the pump is running the pipe will get warm, then hot if it is successfully moving hot water out of the boiler and through the heating pipes.

Why Might Multiple Heating Zones All Run at Once When Only One Thermostat is Calling for Heat?

If all of the heating system's valves stopped working some time ago, someone may have latched them in the "open" position  - so if any of the thermostats called for heat, every heating zone would receive heat even though only one thermostat is calling for heat.

See ZONE VALVES, HEATING for details about zone valve operation, inspection, diagnosis, repair. There we include photos including a zone valve control lever on the side of a Honeywell valve - in the auto position.

If you see that the manual zone valve control lever is "latched" into the "on" position, try un-latching it and then watch to see if the valve operates (and the lever moves) in response to a call for heat at that zone.

See HEATING LOSS DIAGNOSIS-BOILERS diagnostic links if this is the case.

Watch out: hot water may be circulating in a hydronic heating system even if no thermostat is calling for heat, for example if a Flow-Control check valve has stuck in the open position or has been left manually open. See CIRCULATOR PUMP WON'T STOP RUNNING for details.


Continue reading at CIRCULATOR PUMP LEAKS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

If you are not getting any heat at all out of a cold baseboard or radiator, see COLD HOT WATER BASEBOARD / RADIATOR.

Or see these

Hot Water (Hydronic) Heating Boiler Circulator Articles

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CIRCULATOR OPERATION CHECKS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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