HELP. Need help with a vapor lock in a complex system

verulam

Picture and diagram to follow. Pretty sure I have a nasty vapor lock on a complex system that has run well for 10+ years.

The pump supplying my hot water heater shorted out. Being the weekend before X-mas, I decided to swap out the pump from a less important zone. I shut off all the valves, replaced the pump, and bled the system using the automatic and manual air releases. Now I have no heat at any zone.

The system has a square main loop. At the bottom, there is a T that feeds a 90 degree that supplies a manifold for the supply side for each zone (similar setup down stream for the returns). When the boiler fires, I can feel the heat moving down the main loop but it will not move through T where the supplies are.

I checked the controls with a multi meter -- no problem.
I checked the circulating pumps (actually pulled one pump) -- no obvious problem.
I check the micro bubbler and cleaned all the crust out -- seems to work.
The system has static pressure of at least 12lbs.
I closed the return on the boilers, opened the flow control valve, and forced water through the supply to the boilers.
If I crack the drain at the return for a zone, water will flow through the supply. But, when I close the valve and open the return for the zone, the circulation stops.

At this point, I have closed off all the zones. I am just trying to get to zones going that are on the same floor and within 10 feet of the boiler.

Any help appreciated.

motoguy128

Have you tried isolating one zone at a time and trying to get flow? I’d work on purging before you bother firing the boiler. Convective movement can sometimes be opposite of what the pump is trying to do. Bleed it cold and get some flow going first, then turn on the boiler.

Also, how tall is the building? If this is a basement and its two story, 12psi may be marginal once there’s air in the system. Not enough for auto vents on the top floor.

verulam

I am trying to isolate two zones in the basement which are on the same floor as the boiler and only a few feet away. Letting the boiler cool now and will make another rum at it. Not sure how to know there is flow if all the water is cold. Ideas?

neilc

captain obvious here,
I see a lot of closed valves in that picture you posted,
that picture is you in the middle of troubleshooting and purging, right?

EdTheHeaterMan

OK you need to purge the air from the system. I'm not sure if you have the valves I pictured here, but if you do this will be easy. The process should be done in the correct order so you don't have a major water flow problem on the boiler room floor.



1. You need to isolate the boilers as indicated with the valves on the upper right. The water pressure in the purge process may get higher than the relief valve blow-off pressure.
2. You then increase the system pressure by lifting the "Fast-Fill" lever on the water feed valve (Pressure reducing valve).
3. You then connect a garden hose to the first one you want to purge. (Blow the air out with high pressure)
4. Then you close the isolation valve immediately below (or immediately past) the drain valve in #3 above.
5. Open the drain valve and let the high-pressure water force the air out of the pipes/baseboard radiators/convectors and what have you. (A drain is better than a bucket. the bucket will fill rather quickly and need to be dumped several times.)
6. After the air is forced out you will see a constant flow of water with a bubble or two (but mostly water)
7. Close the drain valve.
8. Go to the next zone pipe drain valve and put the hose on there. follow #3,4,5,6 & 7 above. repeat unit all zones are air free.
9. On the last zone, before you close the drain valve... set the auto-feed valve back to automated (12 PSI.) and let the system pressure drop to 12 before closing the drain valve.
10. Put all the valves in steps 1 thru 7 back to the original operating position.
11. now start the system and see if the heat flows.

verulam

Thanks. Think I get it. Will try in the next couple of hours.