What the ... heck!

[Twowaxhack]

You had two 40 gal water heaters right, poorly piped ? Both a Rheem ?

 

[JG plumbing]

One is a whirlpool

 

[JG plumbing]

The one in the picture thermosyphon for the upstairs tennant. It didn't give her instant hot water it just keeps the time reasonable, where prior it took a long time to get there. Mine the whirlpool is a gravity recirc. It's instant and I love it.

My new house that I don't live in yet is gravity recirc and it's instant. That's the one from 1985 Montgomery ward.

 

[Tom the Elder]

You don't. I did mine two years ago. I taped it and doped it and spun it in,while it glugged. There it sits now, with a new full port ball valve.

JG, I don't doubt that could be done but my very limited plumbing experience tells me that something will go wrong and I won't get the darn thing in until the tank has glugged dry - if then (my experience of problem frequency is no doubt due in large part to little experience and all of it on an old house). I think I will use the pump.

 

[Twowaxhack]

I think I will use the pump.

Let us know how that works out.

 

[Tom the Elder]

There’s a hole in the dip tube to prevent a water heater from siphoning more than a few inches down from the top.

Opening multiple faucets won’t help.

Twowax, I am confused. Trying to visualize what you describe, I still can't see how a hole in the dip tube would prevent siphon. If the drain valve is open and air is let into the top of the tank, whether through hot water pipes or pressure relief valve, the water should siphon. Actually, it seems like the higher the hole is on the dip tube, the easier it should siphon. What am I missing?

That gives me an idea. As an experiment, I will try removing the shower head and blowing into the pipe. Maybe that will put enough air into the tank to start the siphon.

 

[Tom the Elder]

Let us know how that works out.

You bet. Unfortunately, that might be a few weeks. Leaving in a couple days for first vacation in 2 years and might not have time before then.

 

[Tom the Elder]

All, I very much appreciate all of the responses! I hate plumbing but very much enjoy learning from all of you.

I have seen a bunch of Youtube videos on flushing water heaters and read a lot about it, including debate over whether or not it is even worthwhile. Nowhere have have I see or read even a hint of others having this problem. Does failure to siphon happen often or is this just my usual luck with plumbing?

 

[Twowaxhack]

The tank will drain with the relief valve open and the drain open. That’s not a siphon.

The dip tube hole keeps your water heater from siphoning dry if the waters off and a pipe is opened below the tank. An example would be a broken water main.

The tank would siphon until the water level reached the hole in the dip tube, at this point the siphon will break.

This is why point of use water heaters that don’t utilize a dip tube usually have a vacuum breaker piped to above the heater on the cold side.

 

[Twowaxhack]

It’ll never siphon below the dip tube even without the hole. It would suck air at that point. So it would never actually siphon dry.

 

[Duckbutter]

For some reason, when I first responded, I thought the o/p stated the T/P wouldn't open, maybe I assumed that where he was opening the shower instead.

The t & P valve open should resolve the problem entirely.

 

[Twowaxhack]

If that were the case I would suggest replacing the T&P valve if it wouldn’t open. That’s kinda a bigger problem than sediment in the tank, maybe ?