Boiler zone turning itself on at night - ? if it could be zone valve

MassBoilerNewB

Hello,

I have a 19 YO Munchkin 199M gas boiler with 5 zones and 5 separate Lux 1500 thermostats. It was just serviced a few months ago. 4 of the zones are working just fine, but the 5th suddenly started heating up overnight, regardless of the thermostat set temperature. Turning the thermostat off didn't make any difference, nor did removing it from the wall.

I'm wondering if this points to the zone valve as the culprit? We have Taco Zone Sentry model #Za024Q41. Or, could it be an electrical problem else where? I'll probably hire someone to come and repair it, but I'd like to have a basic understanding of the problem before I do. Or, if it's really simple that would be helpful to know, too!

Thanks for any diagnostic or educational guidance you can give,

Erik in MA

STEVEusaPA

You could disconnect the end switch wires to see if that helps. But it sounds electrical.
Is the zone heating up and it’s calling for heat or is another zone calling for heat and you’re getting heat in that zone too?

ratio

If the zone valve weren't closing properly, it would heat any time another zone was calling.

I'm hard pressed to think of an electric failure that would intermittently open the valve & fire the boiler. It's possible, but not very likely. Extremely unlikely.

JUGHNE

If the Tstat cable was defective and shorted....sometimes....it would turn that zone on.
Maybe that zone is always on and only noticed at night.
If the tstat wires are disconnected at the boiler that would eliminate that possibility.

schummer

I'm kind of in the same boat. Mine sometimes came on when it was 90 degrees outside. Turned out in my case it was faulty thermostat. Replaced the thermostat with a Nest - all OK now.

MassBoilerNewB

Thank you all for your generosity in responding so thoughtfully, this is an amazing community!

SteveUSAPa, ratio and JUGHNE - I think you may be right, it may be that the valve is open and thus it's heating whenever another zone calls for heat.

I did an experiment - the renegade zone is off right now. I went to check all the other zones and yes they are also off. I turned on a different zone and now the renegade zone is starting to heat up.

Does that confirm that it's the zone valve being stuck in the on position? Are those easy to replace?

Thank you again!!!

Erik in MA

EdTheHeaterMan

Those valves use a battery to close the valve and power to open. How old is the zone valve actuator? May need to replace the actuator. I learned this after having a similar issue and reading the literature on the product. Your battery may not hold a full charge anymore. Try swapping heads with another zone and see if the problem follows the head. I believe the screw-in terminals just unplug making for easy replacement

mattmia2

At least on the modern ones the wiring is just 2 Phoenix connectors that plug in and there is a metal clip underneath the power head you squeeze in toawd the valve and it just pulls off, really easy to swap, doesn't even require tools. (I assumed it was a big capacitor that actuated the valve, but it is essentially power open and power close from some sort of internal energy storage). You can tell if it is open or closed by the position of the knob.

MassBoilerNewB

Thanks, Ed - As far as I know the actuator battery hasn't ever been changed - we've only owned the house for 3 years, and the boiler itself is 19 years old now.


@mattmia2 , I have been wondering why the knob position is slightly different on the malfunctioning valve. I thought 'surely it can't be that easy'. Here's a picture of the malfunctioning valve, on the right, and a correctly functioning valve, on the left - do I just need to turn the knob on the malfunctioning right side? Lol if that's the case.



Thank you both very much!!

Erik in MA

Zman

The knob is for manual operation. It looks like the one on the right is stuck partially open. If you push the clip on the bottom, the head pops right off. You can then check that the valve operates correctly without the power head.
I'll bet you need a new head.

mattmia2

You could give it a try and see if it stays fixed, it could be just that it is mechanically stuck, but i suspect the issue is whatever stores the energy to close it is bad and it will happen again soon if not immediately.

EdTheHeaterMan

@MassBoilerNewB The batteries charge from the system automatically using the electric current from the transformer that operates the zone valve(s). The batteries will lose the ability to charge over time.

MassBoilerNewB

Ok, I did @EdTheHeaterMan's experiment and switched the malfunctioning zone valve to another zone. Now both zone's are working properly! I suspect you are right, that something is worn out in the malfunctioning zone, or perhaps there's a loose wire, but for the time being they are working well and I have a much better understanding of my zone heating system. Thank you all so much for your help, I really appreciate it!

Erik in MA

HomerJSmith

I guess I'm late to the party!

Yes, the one on the right is partially open. When the bar on the knob is perpendicular to the flow thru the pipe like the one on the left, the valve is closed. If the bar is parallel to the flow the valve is open.

The power head has a charging capacitor that is charged from the transformer as Ed says. A capacitor is really a battery, it hold a charge.

You can manually open or close the valve by depressing the knob and rotating it.
Make sure the two plugs are fully inserted in the valve head.

You can switch the power heads by removing the plugs and grasping the power head and rotating it and lifting up. I would switch the power head on the right with the one on the left to see if it still acts up. Just make sure that the plugs are placed back into the power head in the right socket. The plug on the right in your photo is the transformer power plug from the thermostat that operates the valve and the plug on the left is the end switch that turns on the boiler.

Switching the power head will tell you if the power head is the problem.

The green Led between the plugs, when blinking indicate that the capacitor is charging and a solid green light indicates an operating open valve. If there isn't a green light, there is probably a wiring problem or the valve isn't turned on by the thermostat.