Temporary Surge (After Running/Closing Hot Water)?

[lrk1993]

Hi All,

Im wondering if I need to install an expansion tank on my water heater, but I'd like to hear your thoughts first regarding the issue I've been experiencing.

The house is 125 years old (I've lived here 2 years). The plumbing (copper) is from the late 70's, and is still in decent shape. We're on rural water and there is no PRV on the incoming water line (at least not in the house). The water heater is a 40 gallon Richmond propane (6G40-32PF1).

Ever since living here, we'll get an occasional 2-3 second surge (on both hot and cold lines). I've finally pinpointed that it only seems to occur after running a decent amount of hot water (think a hot shower, or extended use of kitchen sink hot water). After shutting off the water to the shower, for example, you can go to any other faucet in the house, and the handles give some operational resistance and the surge occurs once opened.

I tested the pressure last year while in its non-surge state, and it registered 55 PSI.

This plumbing setup has been in place for many decades (excluding the water heater which is 10+ years old), so it can't be too terribly damaging, but I do have occasional drips from some faucets after shutting off (from what I can only assume is due to the occasional overpressurization of the system).

Any thoughts on what my issue may be?

 

[Twowaxhack]

Put a gauge on a hose Bibb and turn it on. Then run about 15 gallons of hot water. Close off faucets and turn off the ice maker of you have one.

Now watch your gauge as the water heater heats with all other water off. If the gauge rises then you need an expansion tank, if it doesn’t then you don’t.

 

[lrk1993]

Put a gauge on a hose Bibb and turn it on. Then run about 15 gallons of hot water. Close off faucets and turn off the ice maker of you have one.

Now watch your gauge as the water heater heats with all other water off. If the gauge rises then you need an expansion tank, if it doesn’t then you don’t.

I follow the instructions you kindly supplied...

Baseline pressure was 60 PSI. After running a good amount of hot water and shutting off, PSI climbed to 170.

Seems obvious at this point an expansion tank is necessary. What size tank would you recommend I use?

I'll have to do some research online as to the best placement of the tank, as my water heater has ductwork right above it.

 

[Rossando]

2gallon or 2.5 gallon is sufficient enough. Make sure you put it on the cold water supply pipe. Orientation should be positioned like so

 

[lrk1993]

I went out to the rural water meter pit, and there is what appears to be a regulator down there. I assume this has no bearing on my issue and the likely solution would still be to add an expansion tank to the water heater?

 

[wpns]

Any system with a regulator or vheck valve needs an expansion tank

 

[Twowaxhack]

I follow the instructions you kindly supplied...

Baseline pressure was 60 PSI. After running a good amount of hot water and shutting off, PSI climbed to 170.

Seems obvious at this point an expansion tank is necessary. What size tank would you recommend I use?

I'll have to do some research online as to the best placement of the tank, as my water heater has ductwork right above it.

The smaller 2gal tank would be fine.

The tank orientation doesn’t matter.

The placement of the tank doesn’t necessarily have to be at the water heater, it just needs to be downstream of any check valve in the cold water piping.

 

[TomFOhio]

It looks like you might have room to put a tee in above the shut off valve and then strap the tank up. When you put your guage on
the spigot does it go up in pressure while no water is being ran?

 

[lrk1993]

So I'm happy to report that the expansion tank install went well. Before adding it, pressure would climb to 170 PSI, now the highest it gets is 75 PSI (baseline is 60).

Thank you all for the help!

 

[lrk1993]

After multiple drains and refills of the water heater with showers this evening, maximum spike pressure registered at 80 PSI, which from what I understand, is about as high as I'd want to have in the system.

Given these are just temporary spikes that get relieved the next time the hot or cold water is cracked opened, maybe the 80 PSI isn't as big of an issue (as compared to a constant 80 PSI, with no spikes)?

I'm not too terribly familiar with the workings of the expansion tank. I filled it to 60 PSI prior to install (to match baseline water pressure of the house). Would adding a few more PSI bring down the spike pressure some, or is that not advised?

Regardless, a reduction from 170 PSI to 80 PSI is still a massive improvement in my book.

 

[Twowaxhack]

The water must be off and the pressure relieved from the system then you add air to the water pressure setting of your PRV valve.

Your PRV valve may be letting the pressure creep up. Monitor your pressure when your water heater isn’t heating.

 

[lrk1993]

The water must be off and the pressure relieved from the system then you add air to the water pressure setting of your PRV valve.

Your PRV valve may be letting the pressure creep up. Monitor your pressure when your water heater isn’t heating.

Thanks...after doing some additional reading, it seems consensus is that tank pressure must match baseline pressure to avoid any premature damage, which it currently does, so I'll leave it alone.

I put one of my cameras on the pressure gauge since the expansion tank install, and when not drawing large amounts of hot water, pressure is a consistent 60 PSI.

 

[lrk1993]

So I went down to check the max pressure on the gauge this evening, and to my surprise, at some point during the day, it had peaked at up around 170+ PSI.

This surprised me, because generally speaking, the max pressures upon tank refilling were around 80 PSI the last few days.

Any thoughts as to how/why I'd see such a large spike, even after the expansion tank was installed?

 

[Twowaxhack]

If you have solenoid valves like on an ice maker or a washing machine or dishwasher it can be water hammer.

Or your PRV isn’t regulating properly.

Or your expansion tank is defective.

I vote for number one but you’ll need to do some checking.

 

[lrk1993]

If you have solenoid valves like on an ice maker or a washing machine or dishwasher it can be water hammer.

Or your PRV isn’t regulating properly.

Or your expansion tank is defective.

I vote for number one but you’ll need to do some checking.

We do have both an ice maker and a washer. There are Sioux Chief water hammer arrestors on both the cold and hot inlets.

Would a bad PRV be symptomatic only when the water heater is drained and refilled? Or would it surge independently outside of heating/expansion of the water heater and I just need to watch the pressure gauge closer throughout the day? The PRV is in the meter pit, which I assume would be my responsibility to replace (and not the rural water company). It's about 3.5' underground and in a tight space, so replacing that would probably be a nightmare of a job.

Expansion tank being defective, would I be able to tell by just checking the air pressure in the tank, or what is the best method? I hope that 170-180 PSI that the max dial registered wouldn't damage/blow out the tank diaphragm.

What is just really puzzling is that after a hot shower or large hot water draw at the kitchen sink, the pressure doesn't exceed 80 PSI (that I've ever seen). Where as prior to the expansion tank install, running 15 gallons of hot water at the sink drove the PSI up to around 180 within 5 minutes.

 

[Twowaxhack]

If your expansion tank is working then it’s a defective PRV or it’s water hammer.

Check the air pressure in the expansion tank with the water off and the system pressure relieved.

Check for water hammer by making the appliance run and cut off while watching the gauge.

If it’s the PRV the pressure can creep up at any point in time, nothing to do with hot water use.

 

[lrk1993]

If your expansion tank is working then it’s a defective PRV or it’s water hammer.

Check the air pressure in the expansion tank with the water off and the system pressure relieved.

Check for water hammer by making the appliance run and cut off while watching the gauge.

If it’s the PRV the pressure can creep up at any point in time, nothing to do with hot water use.

Got it, thanks. With that said, the pressure buildup directly linked with the water heater (in my eyes) justified the install of the expansion tank, so I'm still glad I did that. But it does seem something else is going on.

If I test the washer and cut the water supply at the inlet valves, and I get a pressure spike, what would the remedy be outside of the already installed arrestors?

Then finally, instead of replacing the meter pit PRV, would it be acceptable for me to splice one in on the water main that comes into the basement? So essentially 2 PRV's but the new one would regulate effectively compared to the old one?

I might put a camera on the pressure valve overnight or while I'm out on the weekend, to see if it spikes outside of the water heater refilling.

 

[Twowaxhack]

I wouldn’t leave a bad regulator in the system, I’d remove it. Some water providers service the PRV, most don’t though but it’s worth checking on.

Water hammer can be controlled with the water hammer arrestors that are working properly and reducing the volume of flow the appliances uses. That means throttling the valves down. Throttling valves isn’t really recommended but it can work.

 

[lrk1993]

I've yet to put a camera on the pressure gauge, but it registered with a max pressure of around 85 PSI the last three days until sometime this evening.

What is odd is the max needle registered just under 20 PSI this evening, meaning the max needle made nearly a full revolution. There is no way the max needle can move counter-clockwise when the black needle is behind it

No significant surging at the faucets has been observed since the expansion tank install. I almost wonder if there is in fact a water hammer effect taking place somewhere in the system and causes the black needle on the gauge to "flick" the red max needle significantly higher than what the actual max pressure is.

 

[Twowaxhack]

Yeah that’s what it’s doing. Water hammer popping the red hand