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How to repair a Weil McLain CG Gas boiler

Wm1.jpg (19116 bytes)Click on This thumb nail to see a larger picture of this Weil McLain Boiler that I made repairs to.
 This May look familiar to you If you have an older Weil McLain Boiler.
 In the following pictures I will show How I made the repairs to this Boiler. The Call was No heat in the upper zones. When I arrived I found the boiler hot and The pilot light on.
I also noticed that the pump was working. All of the zone valves were in working order and were open.
The boiler was working normal. So I checked the gauge and found there was no pressure in the boiler.
Why was there no pressure in the boiler? This Boiler has a filtrol expansion tank and fill valve. the tank and fill valve work together to keep the pressure in the boiler. The pressure should be between 12 and 20 PSI.

So I checked the pressure in the expansion tank (the gray tank between the boiler and the water heater) I found it had no pressure, so now I know the tank is bad and needs to be replaced. but just to be sure I pumped some air into the tank, and as soon as I did water started to go into the boiler, I could have just pumped it up to 12 pounds and called it a day, But it would not have lasted long and it would have failed again. And once water was added to the system the leaks showed up. So now I will show you the rest of the pictures and explain what I did to solve this problem.

wm2.jpg (25425 bytes)This is a picture of the tank and the pump I used to pump it up. Before you start with this project. Stop and Think About what it is worth to you and how much money it saved you. And make a donation to this web site. Thanks 

wm3.jpg (24431 bytes)The first thing to leak was the dielectric union on the return side of the boiler just above the Circulator pump.

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and the one on the supply side and the Auto vent leaked from the top and would not stop.  So now I have 3 leaks and a bad Expansion tank. you may have noticed that the expansion tank is stuck behind some pipes and is between the boiler and the water heater, This is never fun.

wm5.jpg (16170 bytes)FIRST turn power to boiler off. then turn the water to the boiler off. then hook up a hose to the boiler drain at the bottom of the pipe tight in front of the bad expansion tank.

wm6.jpg (25404 bytes)wm7.jpg (22939 bytes)wm8.jpg (26787 bytes)Then I removed the auto vent to allow air to come into the top and allow the water to drain out.  After all the other work is done I will install a new auto vent to solve that problem.


wm9.jpg (18722 bytes) wm10.jpg (18915 bytes) wm11.jpg (27716 bytes) wm12.jpg (27348 bytes) wm13.jpg (25873 bytes) 
In The Above Pictures I show how to replace the washers on the dielectric union. Now sometimes the nut will loosen up wit just a few solid taps with a hammer and a big pipe wrench and some times it just will not come apart and you have to replace the whole union. In this case the nut came loose. Once I have the nut off I remove the old rubber washer And clean All of the remaining washer parts from under the nut. (you have to make sure there is nothing stuck in the nut) Then I split the red sleeve and put it over the top of the flange and under the nut and put the new rubber washer between the union then Tighten the nut. This repair is done.
Now the dielectric union on the return side above the pump.

wm14.jpg (28628 bytes) Well this "so and so" will not come apart. I tried everything including heating it with my torch, But it would not give. I have to remove it. So I cut the copper above the union removed the two nuts and bolts holding the pump flange to the pump and through it all away, Put in a new flange and tied back to the copper with a male by copper adaptor and did not install a new dielectric union on this boiler (a dielectric union is not needed here anyway).

wm22.jpg (22392 bytes)Well Now all that is left is to replace the expansion and fill valve (the Filtrol System) normally This is a simple and fast thing to do. But This bad design on the part of plumbers everywhere causes this to be a big deal. 


wm15.jpg (22491 bytes) As you can see There are pipes in front of the tank and a water heater to the left and the boiler to the right and the floor on the bottom and pipes on the top. What the hell was The person who installed this tank thinking? Must not have been thinking at all. The sad thing is I see this exact setup every day.


wm16.jpg (18178 bytes) Ok So the tank unscrewed easy and is now sitting on the floor



wm17.jpg (18345 bytes) I removed the handle from the boiler drain so that the fill valve part of the Filtrol system Will turn.
The copper water line is attached with a compression fitting so I just loosened the nut and pulled the copper out and held it out of my way

wm18.jpg (14670 bytes) Oh Great even with the fill valve removed and the handle for the boiler drain gone the tank will still not fit between the pipes. I can not remove this tank, And I can't get the new one back there either.
So not A new and better plan.


wn19.jpg (18310 bytes) So I stand the old tank up and push it back out of the way. (it will stay there till the boiler or the water heater heater is replaced) now with some 1/2" black nipples and fittings I run the pipes in a different direction, facing the front of the boiler 


wm20.jpg (26559 bytes) I install the new filtrol fill valve (this comes with the new Tank) by the way this is a 110 filtrol If you need to buy this, It looks like the # 30 expansion tank, But it is different and they are not interchangeable. Then I tie the copper line into the new fill valve.




wm21.jpg (16055 bytes) Then I screw the new tank on to the fill valve. Now if it has to be replaced in the future, it's right there in the open, like it should have been in the first place. Now I put in the new auto vent. and turn the water back on.

But I do not turn the power back on yet because the system is full of air and needs to be purged.


wm23.jpg (25327 bytes) This is a picture of the return side of the boiler. I have opened all the zone valves manually and turned all of the red valves off. I hooked the hose to each of them one at a time and opened the boiler drain about half way (you don't want to let it run out faster then it goes in) 


wm24.jpg (25236 bytes)What I like to do is put the other end of the hose into some kind of clear bucket so I can see the air coming out of the lines and I let the water continue to run till I don't see air bubbles coming up from the bottom of the bucket. After this has been done to all the zones. Put the hose on the highest boiler drain or the one furthest from the pump. start letting the water run from the boiler drain then open the red valve ( yours may not be red) and then close the zone valves and let that run till there is no more air. Now you can open all the valves and turn the power to the boiler back on. Find a local Plumbing and Heating contractor