Proper process for draining pipes for PRV or water heater and how to turn water back on

[DoofusOfTheDay]

I am in need of a new PRV, well I think so I have seen a few times now where I turn on master bath vanity or shower and there is a rush of water and it takes a little more effort to turn on water like there is built up pressure. I am also close to needing new water heater. Water heater getting corroded where pipe connects to water heater.

My neighbor, and I've heard of others, had issue with pipes bursting when water was turned back on after they had PRV or water heater replaced. My neighbor said the plumber just turned on water full power and she heard a giant bang in her master bathroom, and sure enough a copper pipe elbow came unsoldered.

A. What is the proper process for draining house pipes for PRV or water heater. Like do you open all faucets, or just the cold? Do you need to flush toilets after water turned off?

B. What is the proper process for turning water back on for all of house after replacing PRV or water heater? I've always thought you leave all faucets open and open water supply to house just a little until water is flowing through all faucets, and then you slowly increase volume to house until fully turned on. Then you can close faucets one by one.

Thanks!

 

[Reach4]

Sounds a little cautious to me, but starting slow should not hurt. That pipe that came unsoldered was probably likely to fail anyway, so having that occur while somebody is around to pay attention was good I suspect. If you have a softener that is not already full of water, let that fill slowly. If you have an upflow calcite (etc) or backwashing filter, start slowly and let the air out. For some things there would be air, and that would come out fast. Dealing with that would be more turning on the faucet slowly rather than turning on the whole-house valve slowly.

The important one is that you need to open a hot water faucet to let air out, and let a water heater, especially an electric WH, fill before turning the WH on.

I think so I have seen a few times now where I turn on master bath vanity or shower and there is a rush of water and it takes a little more effort to turn on water like there is built up pressure.

Regarding that more pressure thing, that could happen if you turn on the WH and then open a faucet. Pressure can build to about 150 psi potentially in that case. If your pressure did climb high after turning on the WH, you need a working thermal expansion tank, and you don't have one. A thermal expansion tank needs to be big enough. There are tables and calculators that help you pick one that is big enough. So have the WH install include a new good thermal expansion tank.

I wouldn't think that just replacing a PRV would need a lot of extra care turning on the water, since you don't have an empty WH or softener to be concerned with.

Regarding draining pipes before replacing a PRV, that will depend on the plumbing in the house. If the new PRV is going to be soldered in, the pipe will have to be free of water. If it is compression or uses a union and threads, a little residual water won't hurt.

I am not a plumber.

 

[Sponsor]

 

[John Gayewski]

Turn your toilet supplies off. I recently ruined my fill valve with a burst of accelerated air. Which has never happened to me before, but the fill valve was pretty old. I think age was a major factor there.


Open the upper most fixture that has hot and cold taps, into the middle position so that the hot and cold piping is open to atmosphere. Preferably a lavatory. Then you can drain down the system. Leave that fixture open when you fill.

I like to leave a port on the water heater open while filling it for a fast fill, when it gets close to full I close the open port on the water heater and slow the filling process. Then go upstairs and wait for the air to stop coming from the lav. Go a little longer to get and solids that have busted loose. Remove the aerator from the lav and clean it, it's possible you'll want to tremor the aerator first depending on the type and state of your system. Then slowly turn the toilet supplies back on.

Its possible other fixtures may need the internals cleaned after this. Shower valves and what not.

 

[DoofusOfTheDay]

Sounds a little cautious to me, but starting slow should not hurt. That pipe that came unsoldered was probably likely to fail anyway, so having that occur while somebody is around to pay attention was good I suspect. If you have a softener that is not already full of water, let that fill slowly. If you have an upflow calcite (etc) or backwashing filter, start slowly and let the air out. For some things there would be air, and that would come out fast. Dealing with that would be more turning on the faucet slowly rather than turning on the whole-house valve slowly.

The important one is that you need to open a hot water faucet to let air out, and let a water heater, especially an electric WH, fill before turning the WH on.

Regarding that more pressure thing, that could happen if you turn on the WH and then open a faucet. Pressure can build to about 150 psi potentially in that case. If your pressure did climb high after turning on the WH, you need a working thermal expansion tank, and you don't have one. A thermal expansion tank needs to be big enough. There are tables and calculators that help you pick one that is big enough. So have the WH install include a new good thermal expansion tank.

I wouldn't think that just replacing a PRV would need a lot of extra care turning on the water, since you don't have an empty WH or softener to be concerned with.

Regarding draining pipes before replacing a PRV, that will depend on the plumbing in the house. If the new PRV is going to be soldered in, the pipe will have to be free of water. If it is compression or uses a union and threads, a little residual water won't hurt.

I am not a plumber.

I do have expansion tank on water heater currently, so that's good I guess.

 

[DoofusOfTheDay]

Turn your toilet supplies off. I recently ruined my fill valve with a burst of accelerated air. Which has never happened to me before, but the fill valve was pretty old. I think age was a major factor there.


Open the upper most fixture that has hot and cold taps, into the middle position so that the hot and cold piping is open to atmosphere. Preferably a lavatory. Then you can drain down the system. Leave that fixture open when you fill.

I like to leave a port on the water heater open while filling it for a fast fill, when it gets close to full I close the open port on the water heater and slow the filling process. Then go upstairs and wait for the air to stop coming from the lav. Go a little longer to get and solids that have busted loose. Remove the aerator from the lav and clean it, it's possible you'll want to tremor the aerator first depending on the type and state of your system. Then slowly turn the toilet supplies back on.

Its possible other fixtures may need the internals cleaned after this. Shower valves and what not.

Interesting on the toilet. I do recall last time we had the water off flushing a toilet was rather bangy and noisy, so maybe this time shutoff water supply and turn back on after.

 

[Jadnashua]

A properly done soldered connection should hold over 200opsi pressure...IOW, it should never 'blow' out with any domestic water supply pressures available!

The best thing is to open any valve slowly. The water velocity will be the same, but the momentum will be much lower getting to the opening...same idea as leaning into a wall versus running into it...you don't really want to run into the wall, same with the water column now being forced through the pipes. That means going around to any valve in the house and individually opening it slowly the first time until you purge all of the air out.

On a pressure balanced shower valve, those initial variations could jam the spool valve, and may take some playing around to free it up. That shouldn't happen if it's in good working condition, but as they age, the seals get stiffer, and some mineral deposits can prevent them from moving freely throughout their full range.

The seal on some toilet valves is actually pretty thin, so opening slowly is not a bad idea, either.

As to draining, open at least one valve near the top of the building, and more may be useful, and one down as low as you can go. The upper one(s) will allow air into the pipes so the water can flow, otherwise, it's like holding your finger over a soda straw...might leak some, but not easily or very fast. You want to ensure your WH is turned off, and absolutely totally refilled before you turn it back on...on an electric one, you'll quickly toast the upper heating element (as it comes on first) and, without water around it, it will overheat and melt quite quickly.

 

[DoofusOfTheDay]

I do have expansion tank on water heater currently, so that's good I guess.

I checked my expansion tank by turning off cold water supply to water heater, opening up hot water faucet until pressure gone, and the expanion tank was at zero PSI. I checked my water pressure in closest outside faucet before doing this, and it was at 50 PSI. So I refilled the expansion tank to 50 PSI. I waited a week and just checked, and it is at 0 PSI again, so getting new expansion tank later today.

 

[Reach4]

I checked my expansion tank by turning off cold water supply to water heater, opening up hot water faucet until pressure gone, and the expansion tank was at zero PSI.

Normally the expansion tank should be empty of water, except after you stop using hot water, and the WH heats the replacement cold water.

Knock on your failed tank, and remember the thud sound. Knock on your new tank, and notice it sounds different. Out of curiosity, what is the date code or install date for the failed tank?

50 psi of air in the new tank is the right amount if your PRV is set to 50 or 49 psi. If your psi setting is different, adjust your air precharge.

 

[DoofusOfTheDay]

Normally the expansion tank should be empty of water, except after you stop using hot water, and the WH heats the replacement cold water.

Knock on your failed tank, and remember the thud sound. Knock on your new tank, and notice it sounds different. Out of curiosity, what is the date code or install date for the failed tank?

50 psi of air in the new tank is the right amount if your PRV is set to 50 or 49 psi. If your psi setting is different, adjust your air precharge.

I replaced the expansion tank with one of those sharkbite thermal expansion shutoffs. I also replaced the PRV while water was shutoff. I opened all water supplys just a little and turned on water main a little at a time. A little banging but minor. Only weird thing I noticed was the single handled showers didn't work at first when I turned water back on to the house. Only after I relite water heater and reopened cold water supply to it and hot water to the whole house did the showers start working properly. What is up with that?

 

[Reach4]

Only weird thing I noticed was the single handled showers didn't work at first when I turned water back on to the house. Only after I relite water heater and reopened cold water supply to it and hot water to the whole house did the showers start working properly. What is up with that?

I have a suspicion on that. They have a thermal valve that controls how much hot and how much cold to mix in. If the temperature is low enough to call for all-hot, and there is no hot, then no water. This is just guessing.

 

[John Gayewski]

I replaced the expansion tank with one of those sharkbite thermal expansion shutoffs. I also replaced the PRV while water was shutoff. I opened all water supplys just a little and turned on water main a little at a time. A little banging but minor. Only weird thing I noticed was the single handled showers didn't work at first when I turned water back on to the house. Only after I relite water heater and reopened cold water supply to it and hot water to the whole house did the showers start working properly. What is up with that?

Shower valves are pressure balanced (these days) . They only give as much pressure as the lower pressure side. You only get an equal amount of pressure on either side. So 0 on one side equals 0 on the other side.

 

[DoofusOfTheDay]

Shower valves are pressure balanced (these days) . They only give as much pressure as the lower pressure side. You only get an equal amount of pressure on either side. So 0 on one side equals 0 on the other side.

Yes after some googling found out the same thing. Everything is working great.