Hot Water system Circulation Issues

genericnj

First, I want to say thank you to all who have helped me in the past, I appreciate it soo much.

I have a dual zone hot water baseboard heating system with a gas fired boiler with a single taco 007 circulator pump on the return line and two taco zone valves serving upstairs and downstairs. About 3 years ago the circulator pump died on me and I replaced it along with vent and water feed valve and pressure release valve.

This season I fired up the system a few weeks back and:

1. Boiler fires and heats water for a bit until it is up to temp
2. Pump makes buzzing sound like usual
3. Zone valves appear to open when zone calls for heat
4. No heat in either zone and no sound of water circulating

I immediately assumed it must be the circulator pump so once again I replaced it, this time I noticed during replacement, the impeller spins freely, unlike last time this happened. I replaced nonetheless, refilled the system with water and fired it up, but same symptoms, no circulation. The new pump does appear to make usual buzzing sound, but no water is getting around either zone.

I am at a loss as to what else it could be, any help is really greatly appreciated, thank you!

I noticed there is a red flow control valve near the expansion tank, what is the purpose of that valve and could that be a culprit? if not, what else could be causing the problem I'm describing?

here is new pump:

This boiler is installed in a utility closet on first floor and extremely difficult to access…

hot_rod

most often when you open a system, to replace a pump for example, you need to purge both zones. A single air bubble can stop circulation.

What does the pressure gauge read?

genericnj

Unfortunately the original pressure gauge is toast, but i have one i attach to the drain and it is reading over 10 psi.

I definitely would purge at the baseboards upstairs and downstairs, but it seems the water is just not moving at all.

SuperTech

If you have zone valves then that red flow control valve serves no purpose at all. The circulator shouldn't be buzzing, it should be silent.

Ironman

Zone valves and a flow check should never be together on the same system. You can manually open the flow check by turning the lever on top and leaving it that way.

However, I doubt if that’s your main issue. You’re either air bound or the zone valves are not opening. I’m assuming your circulator is pumping in the right direction.

EBEBRATT-Ed

Check the 3 things @Ironman mentioned.

genericnj

The zone valves appear to be opening as expected (and in fact when i drained and then refilled the boiler and reopened the hand valve for the zones, i could hear the water flow down). Also I think it would be very odd for them both to stop working at same time…

I will try to manually open the flow check valve to see if that helps.

Regarding being air bound, what would be best way to resolve that? Yes the circulator is in right direction, the previous one that was there was working for a few years since I last swapped it out, the new one is behaving identically to the previous one that I replaced thinking it had failed.

Could there be something else not properly triggering the pump or sometthing that is causing the pump to work wrong?

One additional detail bit, when i turn the system off and the power cuts off i hear a brief bubbling water settling sound around the pump — could there be a clog or something like that near the pump?

Thank you all again!

Ironman

Just because you can manually open a zone valve doesn’t mean it’s working. And it could be opening when powered but the end switch not be signaling the boiler to fire.

And yes, two of them could be simultaneously defective. I found it that way on a job very recently.

hot_rod

We need to see more piping to see where purge valve are, or are not :)

Occasionally with zone valves on the return you can get ghost flow up the supply, so the red flo check would prevent that. Maybe it was added? No harm either way.

Zone valves are best on the supply piping.

Ghost flow or thermosiphoning is basically hot water rising up a vertical pipe, colder water falling down. It can happen in a single pipe. The larger the pipe and the more vertical, off the top of a boiler for instance, the more potential for this.

Additional reading on ghost-busting from B&G and Plumbing Mechanical magazine

genericnj

I recorded a short clip of the boiler firing on, the pump appearing to start pumping when a call to heat is made, also shows the piping in more detail.

Boiler fires at 0:45 minutes of the video — apologies about terrible audio…

https://youtu.be/n80rrLGdaaU

Joe Mattiello

is it possible the circulator is flowing in the wrong direction? Make sure flow direction aligns with flow directional arrows on the zonevales. Your pump diagnostics were spot on. If you take the pump out, put 120 volts to it, and the impeller spins, there’s nothing wrong with the pump.

genericnj

Thanks Joe - 100% sure it spins in the correct direction, it has worked for about 2-3 years this way perfectly until the beginning of this season. I thought it had seized so swapped it for a new one, but it is behaving identically to the one I replaced and the one I replaced spins perfectly without any issues and I did test it with a power cable outside the boiler and it seems to work without problem.

I'm kind of lost at the moment, not really sure what else to check or test :( luckily it hasn't gotten too cold yet, I've been surviving on space heaters…