hydronic zone startup question

[fsteyer]

Hi -

on a remodel job I had to drain the water system so it wouldn't freeze up on me during construction. Now I put it back into service I have one zone that simply won't circulate properly.
I have flushed the loop several times, vented the baseboards, etc ... all the usual stuff. I even completely drained the boiler and started from scratch. I even replaced the circ pump of that zone. When I drain that zone hot water runs through it just fine just from the system pressure. When I go back to the circ pump after 10 min or so it seems there is no water circulating and the pipes get cold.
Any suggestions would be appreciated. Thanks

 

[Plumber1]

purge

Is the boiler set up so you can purge each zone?

 

[Sponsor]

 

[fsteyer]

Is the boiler set up so you can purge each zone?

I can purge/drain each zone at the return manifold
thanks

 

[fsteyer]

here is a pic of the setup. So far I have:
1. Replaced the pump flanges. The old ones has seized up ball valves in them. I guess originally they would work as flow back preventers?
2. Installed a new circ pump
3. temporarily hooked the pump up to make sue it gets juice.

Still nothings gets past the pump ???????? when I use the drain just above the pump I circulate hot water just on system pressure with no problem. When I shut off the drain and turn on the pump nothing. The return pipes below the pump are cold and the pump sounds like its running dry.

Thanks for any help since now this is of course MY problem. After all I replaced a few windows, so if the heat does work I must have done it, right?
Thanks again ...

 

[Plumber1]

boiler

Do you have gate valves on the other side of the loops?

Looking at your picture, when you try to purge you are only drawing water out of the boiler and not the loop. Put a gate valve below that purge valve on all the returns so you can do each zone.

 

[Bob NH]

Check Valves?

Do you have check valves in the multiple pump circuits?

It appears that the new pump is pumping down into the boiler. I can't see the other one. Are they both pumping the same way?

When pumps are connected in parallel, they can bypass flow into another parallel circuit if there are not check valves or other means of stopping the bypass. This would be especially the case if you have a bit of air in the new circuit that is restricting the flow.

If there are not check valves, try turning on both circulators at the same time and see if you get heat in both circuits. Or close a shutoff valve in the parallel circuit for testing purposes.

 

[fsteyer]

OK ... thanks guys. Let me try to answer your questions:
1. There are gate valves on the supply side of the loops on top of the boiler.
2. Both pumps (and a third which is for an indirect water heater) pump into the boiler.
3. There are no check valves between the pumps or return manifold. What you see on the pic is pretty much what I got.
4. When all circ pumps are on the problem loop still doesn't flow through the pump.

I hope I answered all questions.

Thanks again ....
BTW ... I enclose pics of the original flange I took out. It has a ball in the opening that doesn't move.
I guess mostly what I don't understand is why there is not water going through the pump when on system pressure I have flow just 1 inch above it at the purge valve.

 

[Bob NH]

Gate valves sometimes fail shut by dropping the gate from the stem. If it is an old one, you might want to check it by taking the top off and pulling the gate and the stem. Ball valves are usually used in newer installations.

I still think you should have check valves to ensure that all of the pump flow goes through the intended circuit.

Is the problem circuit an "upstairs" circuit? It is possible to get a column of air in a vertical pipe that will increase the head necessary to initiate circulation.

Circulators are low-head pumps and lose a lot of head as flow increases. I suggest that you close the gate valves on the other two circuits and see if you can force circulation on the problem circuit. If there is a bubble of air it may take all of the shut-off head of the pump to get it out and you are losing a lot of head if it is back-flowing through the other circuits. I would try this before disassembling the gate valve.

 

[fsteyer]

thanks again ---
yes the problem circuit is upstairs.
The new TACO pump I put it says it has a built in check valve.
Even when I close the suply ball valves on the other two circuits I still get no pump action from the problem circuit. I do hear a lot of air in that loop when I open the purge valve. Maybe it's just too much air???

 

[fsteyer]

just after my last post I occurred to me that I had talked about the built in check valve. I figured maybe it's stuck. So I put in a circ pump without it and now everything seems OK. The problem loop is circulating. I hope it stays that way.
But I'll take your advice and will install check valves and ball valves were needed. Tomorrow


Thanks again and I'll be back if the success is only temporary.
At least I can go home now.

Thanks again .........