Hot water from the cold faucets!

[mikeconte]

hot from cold -- fixed!

Thought i would report back on the fix. Thanks everyone for the advice.

Basically, I isolated the problem to a backfeed from the hot water heater inlet back into the cold water lines. I could tell this was happening because if i shut off the cold inlet to the HW heater after the hot water was warmed up, the problem went away. So it was not crossing over at a faucet.

I had installed a check valve on the water inlet, but it was the swing type and was not working reliably. I replaced it with a plunger type, which has rubber seal and a spring-loaded plunger, and that solved the problem.

My best guess is that the problem existed from the get go, tho it was perhaps less noticable with the smaller 5g expansion tank. In any case, once the tank bladder failed the problem wasn't evident because there was no hot water pushed out of the hot water tank when the cold was run (the tank is on the hot side of the HW heater).

In any case, the high pressure eventually caused the failure of the TPS valve. I replaced both the tank and the valve, and the problem came back. As above, a check valve on the cold water feed to the heater solved it.

Thanks again - this forum is a great resource.

Mike

 

[Jadnashua]

Moral of the story...install the expansion tank on the cold side as the manufacturers recommend, and this wouldn't happen!

 

[Sponsor]

 

[mikeconte]

hot from cold -- fixed!

yep. now if i could only track down the original plumber and tell him that

 

[SteveW]

I may be dense, but I'm just not getting this.

Why would you need a check valve on the inlet to the WH? Seems to me that the pressure would equalize after opening either a hot or cold tap.

Also, what does having the expansion tank on the outlet side of the WH have to do with anything (other than maybe premature wear of the bladder)?

 

[Jadnashua]

When the water gets heated, it expands. If the expansion tank is on the hot side, it gets filled with primarily hot water. Now, open a cold water faucet, guess where that bladder in the expansion tank pushes water - to the opening; it pushes back through the water heater, pushing hot water out into the cold supply.

Put the tank where it is supposed to go, on the cold, and it nominally fills with mostly cold water, so no dilution of the cold with the hot.

In his case, installing a check valve (that worked well), kept the hot on the hot side, and allowed the cold to run from the faucets.

If he had run the entire contents of the expansion tank out, he would have gotten cold eventually, but he had a fairly big one.

 

[Norcal1]

I think the fact that this is a 3 story townhouse may be a factor in all this as well...that's a pretty tall water column...that's a fair amount of pressure bearing down on the bottom floor, where I am assuming the water heater is located.

 

[mikeconte]

hot from cold

When the water gets heated, it expands. If the expansion tank is on the hot side, it gets filled with primarily hot water. Now, open a cold water faucet, guess where that bladder in the expansion tank pushes water - to the opening; it pushes back through the water heater, pushing hot water out into the cold supply.

Put the tank where it is supposed to go, on the cold, and it nominally fills with mostly cold water, so no dilution of the cold with the hot.

In his case, installing a check valve (that worked well), kept the hot on the hot side, and allowed the cold to run from the faucets.

If he had run the entire contents of the expansion tank out, he would have gotten cold eventually, but he had a fairly big one.

Well said! I also don't think you would see this problem if there is no pressure reduction valve at the street feed, since without that acting as a check valve, the HW pressure would never get higher than the cold from the street. But that is a hypotheses...