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57

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1

Friday, April 22nd 2016, 8:13am

Plumbers STUMPED!! Irrigation causing Airlock in Hot Water tank

Hello, I've had a couple of plumbers out here, and they left in defeat, stumped as to what is going on:

Every morning after the sprinkler runs, we have no hot water in the house (no drips, no noise, just nothing coming out of faucet). Cold water is fine. After much research in the forums, I narrowed it down to an airlock being created in hot water line (or electric HW tank) after the sprinklers turn on or off. Reason being, after I open up all the hot water outlets in the house for a while (sometimes hours), the hot water will suddenly 'pop' out and start flowing again.

I've got a 6 zone system, but only use 4 zones. Automatic controller. Run them for only about 5 minutes now everyday around 3:30am, one zone per day (2 zones on 2 days a week). Yesterday I tried closing the sprinkler's shut off valve about 50% to reduce the pressure, but no noticeable change. There's no hot water coming out of sprinklers.

Any ideas what could be going on here? Thanks for your help!

57

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2

Friday, April 22nd 2016, 1:54pm

Could it be that something else is 'sticking'? But if so, what? I see a shutoff valve from the main next to where the sprinkler backflow preventer is, so assume that is coming from the main. After that, no expansion tanks, no other valves I see anywhere.

The backflow preventer is a water pressure vacuum breaker type, could that cause an issue?

thanks!

mrfixit

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Posts: 2,002

Location: USA

3

Friday, April 22nd 2016, 8:36pm

Have you had any plumbing work done lately or sprinkler work? How long have you had the problem?

57

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4

Monday, April 25th 2016, 8:33am

Thanks, no plumbing or sprinkler work done recently. It's been occurring for the entire time we've lived here (1yr), and just recently did I make the connection between the loss of hot water pressure and the spinklers coming on.

I changed the timing to only 5 minutes for one zone every other day, and over the weekend that seems to have worked, but I'm pretty sure that didn't eliminate the problem and don't know why this is happening.

An idea was that it was the heat traps on the hot water heater get stuck open and allow suction out when the sprinkler came on, but only opening up the tank will confirm that.

Wet_Boots

Supreme Member

Posts: 5,145

Location: Metro NYC

5

Monday, April 25th 2016, 11:08am

If you have an expansion tank on the hot water heater, you might be getting a reverse-flow condition when a sprinkler zone turns on. A remedy for this sort of thing is a check valve just downstream of where the system connects, so the momentarily higher water pressure at the heater is not being forced back towards the water meter.

57

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6

Monday, April 25th 2016, 11:32am

Thanks, but no expansion tank, softeners, filters or anything else on the water heater... Could it be the pressure breaker failure?

mrfixit

Moderator

Posts: 2,002

Location: USA

7

Monday, April 25th 2016, 9:21pm

I know this sounds crazy but is it possible the irrigation water is tapped into the hot water line?

Try turning off the inlet valve to the hot water then run the sprinklers. It can't go back down the line with that valve off.

I don't even know if the hot water inside the house would work at all with that valve shut off? Never tried it.

Does the water that supplies your sprinklers come out of the side of the house?

Wet_Boots

Supreme Member

Posts: 5,145

Location: Metro NYC

8

Monday, April 25th 2016, 10:05pm

Even without an expansion tank, you still have the forces that can make for a reverse-flow problem. System design plays into this. Too much flow is what creates the conditions. If you can reduce zone flow, you can experiment, to look for a threshold flow level.

No PVB defect is involved.

Note, that you cannot add a check valve just downstream of the sprinkler system connection point, unless you also add an expansion tank at the heater. The check valve creates a closed system, which makes the expansion tank necessary to protect the water heater from thermal expansion.

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