Pump not working on hydronic system?

[75gmck25]

I turned on my heat today just to make sure it works when the weather gets cold, and it appears the circulating pump is stuck/frozen. When I set the thermostat to call for heat it turned on the flame and then the pump starts humming. The control display shows the water temp and the word "Circulating", but there is no water actually moving. I tried tapping the pump body with a hammer just in case it would break something loose on the impeller, but it didn't start moving water.

I've attached a picture of the Grundfos pump in the system.

Update/Solution? - I may have found the problem. Right before the pump there is an "Amtrol Air Purger". I opened up the bleed valve on the purger and got a relatively small amount of air out, but then the pump started moving water. It looks like there was an air bubble in the system and it had migrated to the pump so that it was not moving any water.

I have an autofill valve that should add water to the system when needed, but maybe there was still an air bubble in the system even after I bled the radiators last winter.

Thanks,

Bruce

 

[nadogail]

IMHO, lt seems your system just needed bleeding.

 

[James-W]

Is the motor actually turning? The system could be air-locked but you need to be sure the motor is actually working. We used to have a boiler and occasionally the system would get air-locked and I would have to bleed it. I did have to replace the motor/pump assembly one time after about 15 years of use.

 

[75gmck25]

Thanks for the comments. It was just a problem with air in the system.

The boiler runs at 100 -140 degrees in normal operation, but was shut down during warm weather the last 6 months. For whatever reason, the trapped air apparently migrated to the pipe right before the pump, so it was trying to pump air, not water.

When I bleed the Amtrol Air Purger it got rid of enough air to get the pump moving water, and then when I manually cycled the autofill valve I could hear it adding more water to the system. I also bleed all the radiators, but immediately got water (no air) at every valve.

Thanks again for the help.

Bruce

 

[danpik]

What is the static water pressure in the system when cold? You may be low on pressure which is why you are getting air in the system. A "normal" home system should be set around 12-15 PSi when cold and maybe move up to around 20 psi when hot. anything lower than 12 PSi can cause air in the system.

 

[Jackfre]

I had nothing but problems with my old Amtrol air separator. I installed a Spirovent and never had another air problem with the system. A good read on system lay-out is Dan Holohan’s “Pumping Away”.

 

[75gmck25]

My system is on standby (keeping water warm, no call for heat) and currently shows 30 psi and about 110 degrees. There is also an adjustable needle on the pressure gauge that points to 40 psi (too high?).

I turned the system on earlier in the week just to check it out, but the weather then warmed up and there has been no need for heat. I'm not sure what the pressure was when the boiler was at room temperature of about 70 degrees, but it was probably lower than the current 30 psi.

Bruce

 

[LS6 Tommy]

Can you post some unit specs? Hydronic systems usualy only run a little over the PRV setting, typically 20# max for a two story buidling. 100°F seems a little low for the off cycle, too.

Tommy