Water Heater Pressure Relief Valve

[rwidman]

For the water which is in compressible, to drain out of the WH, you need to replace the water with air. How does the air get into the WH? If the check valve isn't there and you think the water is coming out of that inlet, where is it going (through the plumbing) and what's forcing it to flow?

Ted

Air will get into the tank when a faucet is opened.

My previous boat's water heater had a check valve built into the inlet adapter. I don't know about my current boat, where I live now I don't have to drain it.

Gravity causes water to flow downhill. That could happen in some installations.


The important thing is to follow the instructions from the manufacturer of the water heater. We don't need to ask why or second guess. RTFM!

 

[O C Diver]

Air will get into the tank when a faucet is opened.

Most of us leave the faucet closed.

So where do you think the water is going?

Ted

 

[bayview]

Before spending money try draining and refiling tank. see if that helps.

 

[Capt.Bill11]

The check valve is unnecessary as the pump has a check valve in the form of a discharge valve built into the pump. Now if you have an accumulator tank that can't handle municipal water pressure, that may be an issue.

Ted

Better to have the check valve than to rely on the one in the pump alone.

 

[jstauffer]

If you look at the diagram, my check valve is on the other side of the T fittings for city water and faucets (just before the water tank). My water pump does have a check valve built inside it also. When we leave the boat for any time, I always try to empty my holding tank and water heater. Emptying the water heater requires me open a ball valve (installed between the check valve and water heater with a short hose to the bilge or bucket) and in order for it to drain I must open a faucet, or in most cases I just flip the lever on the pressure relief valve. It looks to me the only reason for the check valve would be to keep hot water from migrating to the cold water if the pump was turned off and you lost pressure.

Jerry

 

[FF]

The West diagram stinks.

First it would require an adjustable / cleanable pressure regulator dock side.

Most water hoses are not light proof , so the green stuff will be growing all week.

It would require the prudent skipper to turn off the water on departure , even for a few hours , as a leak could easily fill the boat.

KISS , just fill the FW tank and forget about the deck fill unless its spring cleaning time and you are aboard.

 

[Ski in NC]

If boat ties into municipal water, a check valve is necessary whether in the pump or separately. If you use the tank exclusively, then no need.

The west marine diagram is flawed in the same sense as the OP's system. Only reason to have accumulator between pump and check is to protect it from higher muni water pressure. If accumulator can handle full pressure, put it on the other side of the check.

 

[rwidman]

Most of us leave the faucet closed.

The way we find out we are out of water is when we open the faucet and nothing comes out.

 

[HiDHo]

The Watt's T/P valve normal operation information is available on their web site. Valve lifts at 150 psi and 210 degree's, normal to burp out a cup of water when tank is turned on. I think also standard plumbing for inlet water to have check valve to prevent back flow of hot water out of heater. If the water system is rigid, copper piped as example normal thermal expansion may cause the valve to lift. Safe practice is to manually lift the valve yearly, so burping when turned on not a bad thing. Make sure the valve discharge has a hose to prevent scalding or damage to adjacent people or equipment.

 

[jstauffer]

I rarely use the city water hook up as I like to continually use the holding tanks to keep them fresh and clean. My boat does have a pressure regulator built into the dock side hookup.

Jerry

 

[O C Diver]

My trawler only had a check valve at the municipal water connection. All aspects of the freshwater plumbing work as designed without additional check valves. And, my water heater doesn't suffer from incontinence when it's turned on. If you feel you need additional check valves, and the occasional leakage is ok, then there's no problem. Personally, I don't my hot water plumping and WH pressure tested to 150 psi (or whatever pressure the T&P valve opens at) each time I turn the WH on.

Ted

 

[twistedtree]

I think this is a case of "pick your poison".

If you locate the expansion tank on the cold water side and install a check valve between it and the hot water side, you block undesirable hot/cold water mixing, but you leave it to the hot water plumbing to absorb the inevitable expansion when the water goes through a heating cycle. The only expansion space available is stretching of the pipes etc., which of course is limited, then ultimately the relief valve. It would appear this is exactly what you are experiencing. But keep in mind that if your relief valve is opening then your hot water system is reaching 150 psi, which is super high. At that pressure I think you start to risk blowing out plumbing hoses etc.

If you remove the check valve so the hot and cold water can both benefit from the expansion tank, then you get some amount of thermal mixing, but you maintain a steady and civilized pressure level throughout the system.

Personally, I'd pick the latter for certain. There are also ways to create traps that will largely block any thermal mixing.

 

[Ski in NC]

I have no check valve on my heater, and no problem with warm water backing up into the cold side. What would push the hot into the cold side? A mixing faucet? That's got be a minimal effect if at all.

 

[rwidman]

I have no check valve on my heater, and no problem with warm water backing up into the cold side. What would push the hot into the cold side? A mixing faucet? That's got be a minimal effect if at all.

1) More pressure in the hot water tank because the water has been heated and expanded.

2) More pressure in the hot water tank because you turned off the water pump or ran out of water.

Really, this thread has degenerated into pure speculation. If the manufacturer of the water heater calls for a check valve, it should not be removed, it's there for a reason.

 

[Ski in NC]

Without the check the water heater tank will be the same pressure as the rest of the system. When heating up, it may move a pint backwards due to expansion, but what problem would that cause.

Mine and probably most wh tanks have the outlet on top, so if pump ventilates it still stays mostly full, at least enough to cover the element.

There are plenty of things spec'd in systems that are there for stupid reasons. Unless someone comes up with a good reason for this check to be where it is, it is in the stupid category.

Allowing a system to pressurize up to lifting a safety relief valve in normal ops is not a good design.

 

[jstauffer]

Getting ready to leave the boat for a couple of months, but when I get back I think I will remove the check valve and give that a try.

Thanks guys for all your suggestions.

Jerry

 

[BruceK]

Surely those valves are common on HWS tanks, incl domestic ones. My home system has one, you are supposed to exercise(open) it every so often, though I`ve also been told by a plumber to never touch it. In my experience they have a habit of not closing well after being opened, both the one at home and on the boat, and require a couple of opening/closings exercising to seal. I think it might just be doing its job of venting. My pest controller insisted the vent on the externally mounted HWS at home be fitted with a hose leading to the drains to avoid warm water being deposited near the house, it can attract termites.

 

[sunchaser]

Really, this thread has degenerated into pure speculation. .

No speculation from many of us, merely direct observation. My reasons for removing the check valve were as tree noted, didn't want the 150 psi blowing up boat's hot water plumbing after watching TP valve open continually.

 

[FF]

"Getting ready to leave the boat for a couple of months, but when I get back I think I will remove the check valve and give that a try. "

Just moving the pick up for the expansion tank to the HW line will solve the problem'
IF the expansion tank is not water filled.

 

[jstauffer]

What do you mean if the expansion tank is not water filled?

 

[FF]

Cheap crap expansion tanks like some Jabsco have no diaphragm and will be solid water in time.

Their reccomendation is to drain and vent the unit once a month.

Home style units have a diaphragm and air fill valve.

The pressure is set just below the pumps cut in pressure.

Old diaphragms can leak and the accumulator becomes solid water , no air cushion.

So no place for a bit of expanded hot water to go , except out the safety valve.

 

[jstauffer]

Thanks FF

 

[Ski in NC]

"Getting ready to leave the boat for a couple of months, but when I get back I think I will remove the check valve and give that a try. "

Just moving the pick up for the expansion tank to the HW line will solve the problem'
IF the expansion tank is not water filled.

Putting the ex tank on the hw line will solve the SRV burp problem, but will create another.

If you are using cold water only, that section of the system is then isolated from the expansion tank by the check valve. The pump will then short cycle.

 

[ulysses]

I think some are confusing the thermal expansion tank with the accumalator or pressure tank. Two different animals that are similar in design if not size and function.

 

[FF]

Most boats use a single expansion tank as it easily serves both purposes.

The larger the expansion tank (20G is good) the less the pump will cycle off and on and the longer the pressure sensor will last , esp on a DC pump.

With hot water heating there will be an individual tank as heating circ water may have anti freeze in it , that will kill if drunk.