Problem with flow through zone

Harleyfxr

Hello,
I have a boiler with three zones (honeywell).
Yesterday, I had no heat to my second floor but my basement and first floor were fine.
My boiler pressure was approx. 25psi and temp approx. 170 degrees.
All three zones appeared to be working fine but I had a cold return on my second floor at the zone.
I turned off power to the system, allowed the system to cool to approx 100 degrees and attempted to bleed the system.
Basement first, then first floor with no problems but the second floor did not seem to have good flow through the loop ( barely a trickle).
I removed the front of the second floor zone and opened the valve manually but still no difference in flow.
I assumed a failure inside the zone housing so I replaced the entire valve and have the exact same problem.
It is as if there is an obstruction in the loop.
Also, with the system running and calling for heat, if I shut off the power at the emergency shut off switch, I get a backflow up through the zone of hot water.
Any suggestions would be greatly appreciated.
Thank you
Steve

Tim McElwain

Has this been working fine all the time before this happened?

unclejohn

You didn't mention radiators so I guess you have baseboard and you are bleeding the loop at the boiler through a hose bib type valve. Have you had any guest over in the house , sounds like a shut valve or a blockage some where.

icesailor

If it is series looped baseboard and the second floor isn't working, the "blockage" is almost always "AIR". Resolved by a good purge.

Zone valves don't just break. And on the few occasions that they do, you can almost always tell if the valve opens manually.

hot_rod

Or a frozen line somewhere.

Paul48

Get a hose bib pressure gauge, and put it on the boiler drain, to verify your pressure. Is there a means of automatic air removal on the system?

icesailor

"" Or a frozen line somewhere ""

That too. But only in a cold winter where the thermostats get set way back at night and the zone stays off longer.

You never get the whole story.

If you keep the house at 70 degrees during the day, and you designed for zero outside, and it is zero outside, lowering the inside thermostat by 15 degrees (55 degrees) while you sleep is the same as the OAT dropping to -15 below zero.

Harleyfxr

The only check valve is on the make-up water, no differential, expantion tank is properly pressurized, single stage circ.
I was sure to close zones when bleeding and only open one at a time.

I did resolve the problem..Instead of allowing the system to cool down prior to bleeding, I bled the system at operating temperature and for some reason the second floor zone bled normally and is now functioning properly.
I have always believed that it is not a good practice to bleed at operating temperature because of the difference in temperature of the make-up water..Flooding a hot cast system with cold make-up water etc.
Why would bleeding at temp have been effective and bleeding below temp not effective when I bled at the same pressure each time? Odd.
Thank you for your help.
Steve

Paul48

Your pressure gauge is wrong. Heating the water increases the pressure. Get a hose bib pressure gauge and use it on a boiler drain.Also pick up a brass cap. When you remove the gauge, boiler drains tend to drip.

unclejohn

My guess is you didn't bleed it long enough the first time.

Harleyfxr

Thanks again!

icesailor

Hot water boilers get cold water fed in to them all the time. From the return.

If a boiler is connected at the bottom with the cold water, and the return is properly valved to purge through the return, when the water comes back hot, you know that you have purged the air. When you close off the drain and open the purge valve, you can feel the water returning and cool, then, get so hot you can't hold your hand on it. It stays that way when it is circulating,

When you put the boiler feed on the supply to the system, you only purge with cold water and you can never tell when you have circulated the hot water throughout the entire system. The Fill Valve, pressure gauge and purge hose should be within easy reach. So you can operate the bypass lever, and close it if the pressure is getting too high.