Category Archives: Low Temperature District Energy Sharing Systems

Buffer Tank Pump

Heating systems used in the Cheakamus Crossing development use radiant floor heating and fan coils. Water heated in the buffer tank is circulated by a three speed Grunfos pump. When the heating system first starts in the fall it is important to check for proper circulation. The circulation pump has not run for several months and there is a chance that air has built up and can prevent the pump from circulating water and cause the pump to fail.

Image of pump and PEX piping
Buffer Pump and PEX Piping

Turn up a few of the thermostats so several zones will call for heat. Within 5 minutes the pump should start. There may be some gurgling at the start but should stop after a few minutes.   The gurgling sound is from air in the system which is common in many of these units and difficult to completely eliminate.   There are automatic air bleeders installed on the heating system and an air scrubber of the heat pump circulation but do not always work. Some air bleeders are poorly placed or can fail if the vent plugs up.

Air trapped in the system will compress and prevent the water circulation. Without water moving through the pump it will over heat. There are several reasons why the pump can fail but air trapped in the pump has been an issue and happens most often at the beginning of the season or after the pump has been off for an extended period.

It is not obvious on these systems that water is circulating, it may sound like the pump is running but there may be little or no water circulating. You will need to remove the access panel on the first floor to see the radiant floors valve headers. Flow indicators on the top or bottom of the valve header should move on the zone valves that are open. If the actuator is raised and the pump is running, there should be movement on the flow indicator. If the actuator is down then the flow should be zero.

In floor heating
In floor heating

If there is no flow through the pump, the body of the pump will get very hot, too hot to hold your hand on it without burning. These pumps are fairly tough and can handle a little overheating, but if it is left to overheat for several hours will cook the bearings and the pump will have to be replaced.

If there is problem, then call a service technician to look at the system. They may be able to save the pump and correct the problem. There will be a reason for this problem, do not just replace the pump without identifying the issue. These pumps should last ten years or more. If the pump fails and issue is not corrected it will fail again. Some unit have already had this circulation pump replaced 3 times.