Bizarre problem. Solution found. Common behavior?

[Deleted User]

with a standard, mop sink faucet where cold and hot were left on 24/7, but had a garden hose with a spray handle that was used as the off mechanism. perpetual mixing it was

Jim Franklin

Hot water from cold tap, occasionally

For at least a few months I've been getting very hot water from the cold taps throughout the house. It seems to happen at random times, but I notice it more if the heat (steam) has just cycled. I thought heat was radiating from an uninsulated pipe to the cold water line.

Nope. The anti-scald mixing valve for the tub at the farthest reaches of the house is letting hot water from the supply line bleed into the cold water supply line, setting up a giant convecting loop. I used the tub today so the lines were primed for convecting. The burner has been running once an hour to reheat the indirect tank.

Is this an issue with the mixing valve, or did the plumbers forget to put a check valve in somewhere? The mixing valve is a Honeywell Sparcomix.

thanks,
jim

Tom Blackwell_2

Yes, this is a common problem. The internal anti-scald valve seats are located upstream from the shutoff, so a small amount of leakage can occur if there is a pressure differential between cold and hot, such as a hot water recirculation pump.A pressure differential is also present when the indirect tank heats up, thus expanding that volume of water. This happened in the dorms built for the olympics in Atlanta, the whole building has warm domestic cold water. Fix is to add check valves in hot and cold lines going to the valve.

[Deleted User]

Got Moen???

Moen single lever valves are notorious for creating cross connections betwixt the hot and cold lines.

Now, on the other hand, some people pay good money for a DHW recirculation return system. You got yours for free!!!

ME

PS, Keep a pitchure of cold water in the refrig for drinking...

ME

Unknown

bypassing mixing valves

I'm not certain that I understand - You say that the mixing valve on the tub is bypassing. This is a common problem with tub/shower valves that use a diaphragm for pressure balance. The diaphragm ruptures and allows hot water into the cold water line.

You mention a Honeywell/Sparco mixing valve. I don't think that this valve is the problem. It is most likely the tub/shower mixing valve that is causing your problem.

J.C.A._3

To add...

I've also seen laundry valves that are left open become a nifty little "transfer station" between the hot and cold. With all the rage being laundry services being moved to the upper floor...it just may be something to keep in mind.

Hint: get one of the electric ones (the name escapes me) that only open when the power to the washer is turned on. It would have saved my brother a good chunk of ceiling...even with the drip pan and pipe to the basement.Full pressure to a 3" high pan was a bit overwhelming! Chris

Jim Franklin

I think my terminology is wrong. It has separate hot & cold taps, but under the deck is the Honeywell. It will add cold water to the hot if the incoming hot is above a set point (adjustable from 100 - 145). Anti-scald device that's code in MA now.

If I back it out to 145 I get no cross-flow. But if I screw it in to lower the output temp, it connects the hot & cold supply and gravity flow takes over.

jim

Radman

gravity flow test

Jim,
If I understand you, you have a Sparcomatic point of use mix valve under the tub deck, with a two handle tub filler. If this is the case, run the tub in the morning to create the gravity prime. Shut off your cold supply inlet to your indirect water heater or whatever else you have installed before you leav for the day. When you return at the end of the day, see if the flow has continued. If it has not, you've isolated the circuit. You can install a weighted check valve on a horizontal portion of the cold water inlet to your water heater. Another option would be a thermal trap in you water heater inlet. What kind of indirect tank or water heater do you have?

Home Depot Employee

Check or no check

Assuming you have the domestic hot water unit installed and not the hydronic heating unit, you must have the domestic unit without check valves which should be used.

Whats the model number?