hydronic heat system issues

I have a hydronic heating system (2 zones of forced air, fed from a central boiler). The zones are fed by one central circulator pump on the boiler and Taco 571-2 valves on each loop.

The downstairs loop works just fine but I was noticing poor heat from the second floor loop, so I did a quick temperature rise test on them to confirm it. The first floor furnace got to max temperature (122f) in about 5 minutes of operation and maintained a heat rise of 55-65 degrees after that (65 in, 120 out). However the upstairs loop took about 10 minutes to get to temp and only had a rise of about 23 degrees (62 in, 82 out).

My first thought was air in the loop so I let a couple of gallons out of the upstairs loop using the drain valve thats right before the taco valve. I didn't notice any spitting or bubbling, so I think its ok on that front.

It does seem to be calling for heat ok, because the fan turns on just fine and the boiler burns up. So I'm thinking the thermostat is ok.

My next thought was to try some manual operation of the Taco valve to see if that isnt opening fully.

Anyone have any other suggestions? I have a multimeter and I could test some voltages coming out of the thermostat if I knew what to look for.

 

Your tstat circuit is 24V but if your zone valve is opening on a call for heat that is not your problem.

 

I'm not sure it is. I tried manually actuate the zone valve while the heat was off and it wouldn't go with any reasonable amount of force. I can manually actuate the other zone valve with just a decent push on the lever.

 

Since you suspect a zone valve problem, I suggest checking the temps of the hot water pipes into & out of the coil in the air handler.

 

Air in hydronic systems rises to the highest point in each loop. Venting or draining water near the boiler, usually at a low level, does not remove air in high points.

Vent the upper loop with existing vents. If none, a simple way vent is with a saddle valve. Turn the needle in and out until is just starts to vent air. When water comes just turn it in snugly until it stops. There is no need to turn needle completely in and "bottom" it. As a backup place a pipe cap on the valve outlet.

Sioux Chief 1/4 in. x 1/4 in. Lead-Free Brass Compression x Compression Self-Tapping Saddle Valve-997-940201 - The Home Depot

 

You should be able to manually open your zone valve as you know. If you cannot then there will be a temp. difference as Grady has mentioned but instead of checking it at the coil you should be able to see the difference right at the valve itself. It should be hot before the ZV and if nothing is getting by will be cool after the valve.

If you cannot push it down with the lever try taking the head off and with a pair of channel lock pliers see if you can push the plunger down or if it's frozen. If frozen either body or guts must be replaced.

If you are feeding into an air handler there most likely is a manual bleeder on the coil itself which is all you need. If the coil is air bound you shouldn't have to bleed that much water from it and it should get hot very quickly. If you get all water and it stays cold look elsewhere like the ZV.

Make sure you at least have hot water going to the coil. It sounds like you are not getting circulation to the coil.

Hope this helps.