I have Hydronic Heat, with a Weil-McLain Boiler and an indirect fired Model-100 80 Gallon water heater.   In the master bath when one person takes a shower it takes the normal amount of time for hot water to reach the shower.  After the first person finishes their shower, the next persons shower starts warm and then turns ICE cold for ~30 seconds and then returns to normal. I'm not running out of hot water.  

I have Delta pressure balanced shower controls. While the water is running cold, turning the valve to full hot does not produce hot water for the ~30 seconds.  The home is a 3 story home and the Boiler and Hot water are on the 3rd floor.  The shower is on the 2nd floor.  

The house also has a hot water recirculating line that goes to the far side of the house.  It feeds a 2nd floor laundry and a first floor bath and Lav.  That line has a back flow preventer just above the hot water tank and 2 valves that isolate the recirculating pump to allow its removal.  I've turned off the pump and both valves but the problem continues.

The house also has Well water so pressure is not very constant. It varies between 40 and 60 psi.

It seems to me that somehow cold water is entering the hot water line between showers. Is there a design issue because the hot water tank resides above the shower?  Any ideas how the cold water can get into a hot water line so quickly.  

This is not an issue with exposed pipes.  The cold water happens during 100 degree weather.  The problem is noticeable with just a few minutes between showers.

Hi Jim, I wish you had included a model# For the Delta Shower valve. If I had to guess I would say there is something in the pressure spool that's opening up and diverting cold water direct to the shower head. If it were in your pipes it would be cool, not ice cold. It would be tempered by the mixture of hot water. Butyou already knew that didn't you? I think you did a bang up job of tracking down the problem. If this were my call I would change out the innards of the valve. Good luck, Tom

It's a monitor 1800 with an added hand shower diverter. After the first shower the water runs warm for 15 or so seconds and then turns cold. After 30 seconds it gets warm again. The house is new so its not a worn part. It seems like water is being siphoned backwards but I can't figure out how this could happen.

The other strange thing is both pipes at the hot water tank are warm. I assume the cold feed pipe should cooler than the hot but Im guessing this could also be adjacent heat warming both pipes. I have access to the pipes farther away from the tank so Im going to see what happens to the pipe temps during this cycle.

Is it possible the plumber hooked the monitor 1800's valve up wrong? Does it have more than cold in, hot in and shower out? The flow control is a single lever with a separate knob for temp control.

I'm concererned because if the cold water is flowing back to the hot water tank Im wasting a lot of fuel.

Anthing else that I should look at to trouble shoot the issue?

Thanks

Good morning Jim, Please excuse the delay in answering. My computer was down. The reason the cold water inlet pipe to the water heater is warm to the touch is that the hot water raises to the top of the tank and convection carries the heat through the copper pipe. It's normal. I don't think the plumber hooked you up wrong and I doubt that you have a cross connection allowing cold water to flow back to the tank. What I would do is call the plumber back and ask him to check for an faulty scald guard valve. If that valve's faulty then it would divert cold water out the jets. It may be a bit of trash that has got in the valve or the valve itself may be faulty. Good luck, Tom

I also have a problem with a shower that after warming up turns cold, for up to two minutes and then gradually warms up again. It's a one time thing. Should I have the shower faucett replaced?

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Originally Posted by willie5

I also have a problem with a shower that after warming up turns cold, for up to two minutes and then gradually warms up again. It's a one time thing. Should I have the shower faucett replaced?

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Hi Willie,

What make and model number is your faucet? Is it a temperature controlled faucet? Before we can answer your question we need more details. Get back to us and we'll asnswer ASAP. Regards, Tom