Could use a hand troubleshooting a mystery... leak/flow reported with no physical leak found. Expansion tank or indirect hot water heater issue?

[Rossn]

Apologies in advance for this being lengthy...

I have an odd situation going on. I have a moen flo smart water valve that has shut off the water after detecting 0.1-0.3 gpm flow for 10 minutes 6 times over the last 3 nights... only late at night. It then turns off the water. I've been up for some to check and turn on the water for half of the events, and then it happens again after I go to bed.

It appears to actually be flowing that amount of water, but to where... it appears to be disappearing? Almost all of my plumbing is exposed, with the downstairs unfinished... no notable leaks found anywhere (a gallon of water would be obvious), no sounds of toilets running, and the only drain connected appliances are a dishwasher and clothes washer + toilets.

I am on a 30 year old natural gas cast-iron boiler with a 20 year old indirect hot water heater. Supply side thermal expansion tank is maybe 6 years old.

I need more active events to test, though it did appear that the flow went to 0 when I turned off the CW supply to the indirect last night, then resumed when I turned the valve back on. On a prior event, I turned off the cutoff valve downstream of the smart meter... when I turned it back on, flow went to 0.

Maybe a year ago, Flo reported a thermal expansion tank issue, but that has not reared its head again until today when I ran maybe 30 Flo leak check cycles, and twice in a row I got that message (when I had turned off the DHW manifold valves off).

Since Sep 28, I have been getting drip reports from the meter. Based on today's testing... think it's somewhere on the hot water side of things.

The other notable issue is that the boiler system has been getting notable air in it for the last year and a half... I have not been able to track that one down.

Is there any possibility of a failure on the indirect that is feeding the water over to the boiler (or a bladder failure)? I would think I would see abnormal pressures there, if that was the case.

Sorry for the ramble... it's complex. Thanks for your thoughts on this one!

Moen Alert Times (shutoff 5 minutes after):
Oct 12, 12:43am 6 mins at 0.3 gpm
Oct 12, 11:25pm 8 mins at 0.6 gpm
Oct 14, 1:51am 5 mins at 0.2 gpm
Oct 14, 10:44pm 5 mins at 0.2 gpm
Oct 15, 12:16am 6 mins at 0.2 gpm
Oct 15 1:37am 5 mins at 0.2 gpm

 

[John Gayewski]

You would see high pressure in the boiler and the relief valve would trip on the boiler if the indirect was leaking.

That boiler system should be full anyway so the water can't be going there. It has to be expelled somewhere for it to go through the meter.

An expansion tank should almost no water in it. The air side should be slightly (2psi or so) than your water's supply pressure on a domestic expansion tank.

A boiler' s compression tank should be set the same as the boiler system pressure it could take some water for a time but the relief on the boiler would ultimately give way and show the failure of the prv on the fill system.

 

[Sponsor]

 

[Rossn]

You would see high pressure in the boiler and the relief valve would trip on the boiler if the indirect was leaking.

That boiler system should be full anyway so the water can't be going there. It has to be expelled somewhere for it to go through the meter.

An expansion tank should almost no water in it. The air side should be slightly (2psi or so) than your water's supply pressure on a domestic expansion tank.

A boiler' s compression tank should be set the same as the boiler system pressure it could take some water for a time but the relief on the boiler would ultimately give way and show the failure of the prv on the fill system.

Ok, thanks John. So no indirect leaking across to the boiler (it has a LOT of air in it currently... I need to purge it), will check expansion tank and compression tank pressures. I assume if water comes out, I've got an issue there. Nothing has come out of the T&P yet.

 

[Reach4]

Turn off the valve that feeds the boiler refill.

Do you have a softener? Timed irrigation system?

 

[Rossn]

Turn off the valve that feeds the boiler refill.

Do you have a softener? Timed irrigation system?

Thanks, Reach. I have done some testing with that, but agree that could be suspect and will troubleshoot it. That said, it's been colder the lasts, with the boiler running more, though we aren't actually heating the house yet... just circulating water back and forth to the manifolds.

No softener or RO filter. Irrigation comes off the main line before it reaches the house.

 

[Reach4]

So here is the suspicion: pressure tank is failed or too small. Water heats and pressure relief releases water. Then when the water cools, the pressure drops. The automatic refill valve replaces the lost water. Repeat.

If your pressure refill valve is set to 12 psi, the air precharge should be 12 psi. Air precharge is measured and set when the water pressure is near zero or the tank has been disconnected.

I don't really know hydronic systems, but I am repeating what others have said.

You could start a time lapse movie of the pressure gauge when you go to bed.

 

[Fitter30]

Put a piece of paper under relief valve piping it will show if it gets wet. What is the boiler pressure and temp. With micro bubbler air vent air shouldn't be a problem it will get all the air out is the vent cap loose? Systems under 10-12 lbs if the gauge on fill is correct. Radiate heat shut off and drained?

 

[Rossn]

So here is the suspicion: pressure tank is failed or too small. Water heats and pressure relief releases water. Then when the water cools, the pressure drops. The automatic refill valve replaces the lost water. Repeat.

If your pressure refill valve is set to 12 psi, the air precharge should be 12 psi. Air precharge is measured and set when the water pressure is near zero or the tank has been disconnected.

I don't really know hydronic systems, but I am repeating what others have said.

You could start a time lapse movie of the pressure gauge when you go to bed.

I suspect 'too small' is unlikely, given it's been behaving well for a long time, but certainly something could be failing. I'll check some pressures tomorrow, for sure. Thanks for the ideas. BTW, I have been up when the flow has been happening, and the gauge appears to be pretty consistent, but agreed it could be fluctuating when I'm not seeing it.

 

[Rossn]

Put a piece of paper under relief valve piping it will show if it gets wet. What is the boiler pressure and temp. With micro bubbler air vent air shouldn't be a problem it will get all the air out is the vent cap loose? Systems under 10-12 lbs if the gauge on fill is correct. Radiate heat shut off and drained?

Thanks, Fitter. I will try the paper temp.

There is a mixing valve and outdoor reset on this one, so system temp is dependent on outdoor conditions... lately, it's been in the mid to upper 40's over night. More of a mid-temp setup at the moment... currently it's 55F outside and targeting 113F.

Yeah, have the air bubbler, but either it's not working or too much air to work (I thought I read previously it works better with smaller bubbles, not bulk air). There is a TON of air in the system now, as in gurgling at times while pumping, and I'm planning on purging it out tomorrow. I still cannot figure how it enters the system without leaking water. I suppose on a cool-down cycle it could suck in air.

The system is running around 12psi, if the gauge is to be believed.

As to the radiant status... I just have TRV's set off at the moment as well as one or two manifolds turned off in whole, so there's some circulation via some manifolds, but not all of them... no real emitters getting hot water currently. At least I think that's what you were asking.

 

[Fitter30]

Cast boiler has a minimum return temp 135° Normally my minimum is 140°. Below these temp boiler will condense and drip. Condensate on burners and insulation. Return water would return cold and crack a cast section.
Your boiler might already have a crack in it. Fire boiler run the temp up to 160° while firing listen for sizzling. Water is flashing to steam. Might see the flame coming off burner changing with water hitting them. You might not see the water or the steam even if the water makes it to the bottom of the burner drawer the radiate heat it would vaporized it.

 

[Rossn]

Cast boiler has a minimum return temp 135° Normally my minimum is 140°. Below these temp boiler will condense drip condensate on burners and insulation. Return water could return cold and crack a cast section.
Your boiler might already have a crack in it. Fire boiler run the temp up to 160° while firing listen for sizzling. Water is flashing to steam. Might see the flame coming off burner changing with water hitting them.

You're right Fitter (as always). At one point, I learned the hydronics part reasonably well and even designed the system, but with learning all the other trades on the house rebuild and that being idle on the hydronics for some years, it's not fresh.

I think (will need to go pull the front off to verity) it's still at 170-180 on the boiler itself., but the mixing valve lowers the overall output flow feeding the zones to the temperature by mixing return flow with the outbound flow. You make a good point... with as much air as I have, it is possible. I will check thoroughly to see if what you've described is happening and report back.

As always, thanks for your insight.