Weil-McLain Gold Plus 40: Leak in Heat Exchanger

JAdams

I want to share this with you all. Recently, on a vacation home, I was installing flow checks on the return piping of a system because of convection. At the same time, I was to install a boiler feed tank, because there was no make-up connection. The system was installed about the year 2000. For the past two years, there was excessive air in the system, which I thought was due to there being no fluid feed. I was partially right, however read on.

Every zone can be isolated and purged without having to shut down the entire system. The system had a Weil-Mclain Gold Plus 40, Indirect Fired Water Heater. I drained each zone individually, using air pressure to blow out any excess fluid, to make my job a little easier. As I got to the Water Heater zone and applied air pressure, I could hear gurgling in the tank. Knowing it was a tank within a tank, the sound just didn't seem right to me. So I did some further testing. Able to totally isolate the DWH in every aspect, I closed all ball valves, on the domestic and boiler side. I attached a pressure gauge to the boiler return side of the loop and pressured the the zone with 25 psi of air. The pressure gauge rose to 25 psi, but as suspected, dropped at a steady rate. I then moved the pressure gauge over to the domestic cold water supply, and administered the same test, through the boiler supply pipe. Just as I thought, the pressure in the domestic water supply side of the DWH started to rise. And the last test I administered was basically the same, I just change locations as to where the pressure was being added and measured. I moved the pressure gauge to the boiler return piping and supplied air pressure to the cold water fill on the domestic side, the result was the same thing. I was confident that the Indirect Fired Water Heater had a bad heat exchanger.

Keep in mind that this is a vacation home, the house is heated @ 55 when vacant and to 68 when occupied. The water heater and domestic water is turned off when the house is vacant. Knowing this and all the above, the puzzling thing is this: Why didn't the domestic water pressure (70 psi) override the boiler pressure (15 psi) when the home was occupied? My testing with air clearly proved there was a leak, somewhere between the two tanks. However, the pressure in the hydronic system never rose above 20 psi, that I know of. Being air is lighter than water, I can only assume that the heavier domestic water, was in fact, leaking into the boiler side of the water heater, but at a very slow rate, not enough to raise the pressure. I also think that is was possible that when they were using DHW, it may have siphoned fluid from the heating system, thus causing fluid loss to the heating system, and with no make-up water, creating air pockets.

I did cut part the outer tank and pull the inner tank out. The inner tank is corrugated, however, 1/3 of the the tank was swelled at the bottom, making it very difficult to pull apart. I didn't see any any cracks or pinholes on the inner tank, but I couldn't see the very top part where the nipples are welded to the tank. However, on the inside of the outer tank, I could see rust in one particular spot, that ran from the top of the tank to the bottom.

icesailor

The hidden fact about those tanks are that you have to be extremely careful when you drain them. And fill them.

When you fill them, you must fill the potable water side first, then the boiler/outside. Or else, if you fill the boiler side, the buoyancy of the inside tank full of air, might rip itself from whatever is holding it in place.

When you want to drain the tank, you must drain the outside first, then the inside. They give you a spare dip tube to use to drain the tank to meet Massachusetts requirement that it have a separate drain. Most installers throw the spare drain in a closet or the trash.

The inner tank is thinner than a normal tank. I personally, tried to drain them both together. I was always afraid I might damage the inner tank if I completely drained the inner tank.

Maybe that happened to you. The only way you can drain the inner tank is with compressed air and the hose on the added dip tube for draining.

JAdams

icesailor said:

The hidden fact about those tanks are that you have to be extremely careful when you drain them. And fill them.

When you fill them, you must fill the potable water side first, then the boiler/outside. Or else, if you fill the boiler side, the buoyancy of the inside tank full of air, might rip itself from whatever is holding it in place.

When you want to drain the tank, you must drain the outside first, then the inside. They give you a spare dip tube to use to drain the tank to meet Massachusetts requirement that it have a separate drain. Most installers throw the spare drain in a closet or the trash.

The inner tank is thinner than a normal tank. I personally, tried to drain them both together. I was always afraid I might damage the inner tank if I completely drained the inner tank.

Maybe that happened to you. The only way you can drain the inner tank is with compressed air and the hose on the added dip tube for draining.

Thank you for your input Icesailor. I'm located in Northern NY, right smack in the middle of the Adirondack Mts. When I started this business, I installed several WM Gold Boilers (gas & oil) and Gold Plus indirect fired water heaters. Although it's been quite a few years since I've done the installs, I do not remember the instructions mentioning anything about filling & draining, as you did. I find what you describe about filling and draining quite interesting, however, I do remember WM mentioning that the tee and boiler drain provided are to go on the cold water supply for draining purposes. That the unit is siphon drain only. Interesting enough, in the past, this particular unit has been drained of domestic water only. The outer tank has never been drained, to my knowledge, because the system had hydronic antifreeze in it. I never did like the siphon drain idea because you can never totally drain all the water, without disconnecting it and turning it upside down, because I'm in an area where it's very common for the temperature to drop -0 for a few months. And, not having heat on in a house in those temps, it's not uncommon to see it temps indoor drop to the single digits.

Bob Bona_4

Replaced a 3 year old leaking Smart 50 yesterday. Same mfr. The siphon idea never works for me. I cut a washing machine hose end off and stick the cut end down either the hot or cold (remove dip tube) and pony pump it out. Sometimes, if the tank is a loss and there's a floor drain etc around, I just drill a hole in the inner tank from the lower boiler connection and let her rip.

icesailor

On the installation manuals, read the special instructions for Massachusetts Installations.

The first tanks had the warnings about how to fill them. They may have changed the notification. I never installed any of those tanks.

For those draining them in cold areas, if you drain the tank as low as possible with the dip tube, by blowing it out with air, or sucking it out, the remaining water will not break the tank. If the water freezes, it freezes from the outside to the inside. The expansion will rise up into a dome and the pressure is upward. It won't break the tank. Its the same as a horizontal pipe that is 1/2 full of water. The water may freeze but the expanding pressure has a place to go. If you haven't been blowing out winterized houses and only drain them by drip/drains, and you have never had freeze ups and broken pipes, before you turn it back on, blow out the house with compressed air, like you are going to drain it. You will be amazed at how much water is still in the system. And how much more comes out after you blow it out with air. And you don't have to dismantle the solenoids or break the vacuums on toilet ball cocks.

ageless

Just read your post. Has some interesting points to it but after reading thru what you have done already I believe you have two problems here. It sure seems as though the Plus tank does have some kind of leak in the tank wall or weld however it seems surprising that the crack or pinhole has remained somewhat small till now. The second point I see is your question as to why the domestic water pressure has not driven up the boiler pressure. In the beginning you say in the past year you have had an issue with excessive air in the system and you were to add a makeup water tank. Have you considered you may also have another leak in the system on the radiant side loosing water just enough to maintain a low boiler pressure to match the leaking plus tank. Just a thought may may be worth testing for.

JAdams

ageless said:

Just read your post. Has some interesting points to it but after reading thru what you have done already I believe you have two problems here. It sure seems as though the Plus tank does have some kind of leak in the tank wall or weld however it seems surprising that the crack or pinhole has remained somewhat small till now. The second point I see is your question as to why the domestic water pressure has not driven up the boiler pressure. In the beginning you say in the past year you have had an issue with excessive air in the system and you were to add a makeup water tank. Have you considered you may also have another leak in the system on the radiant side loosing water just enough to maintain a low boiler pressure to match the leaking plus tank. Just a thought may may be worth testing for.

Thank you for your reply. I was baffled as to why the system was losing water. I've pressure tested each zone, that is how I found the problem with the DWH. I assume cross connection was the problem, as it only happened when the homeowners were using the place.

Since then, I've replaced the DWH, added 4 Flow Control Valves and also added another tank, filled with glycol/water mixture as a boiler feeder. Been back to check it twice, all good!

clammy

does your domestic portable water have a portable expansion tank .Im pretty sure that weil insists that one be installed due to volume of water in the portable side of the tank .I know that in the past i have replaced those tanks which did not have them due to thermal expansion over time it will stress the tank plus with out flow chk the law of thermodyanics would cause the tank to over heat putting a tank with out a thermal expansion more suspect to the damages of thermal expansion.Some may say that if the home uses a well trol tank that should be fine but i have allways used thermal expansion tanks on all indirect tanks reguardless of manafacture and have not had any tankks fail due to expansion.I started to stray away from tank in tank designs there where alot of failure espically due to thermal expansion and no one installing them.I see this on standard hot water heates also usually due to hi water pressure and prv or chk valves water main .Being the home is a vacation home and has glycol in the system side has any one tested it s ph For your glycol could have gone acid i would chk that out also .Hope this helps peace and good luck clammy