Weil Mclean Tankless internal Leak?

I have a three year old Weil Mclain WTGO-4 boiler with WT-14
tankless. Last winter it started dripping from to 30psi pressure relief valve.The system had been running fine since its install, with yearly service being done by my oil supplier.When it started dripping the pressure gauge read 30psi I drained out some water to lower the pressure,it was fine for a couple of days then started dripping again. At this point my internet search for info brought me to this forum back in March. This is what I have done so far, first I SHUT OFF the boiler feed water , still dripping from PRV ,I then replaced the PRV a few days later same thing. Water feed is still off, I then figured I would change the bladder type expansion tank an Extrol model 30. I replaced it with the next size larger, a WATTS ETX-60 . After that pressure stayed down and no more problem. That was in April then the heat is off all summer and just using the tankless for hot water .WATER FEED IS OFF TO BOILER ALL SUMMER.
Just this week water is dripping from PRV,pressure is at 30 psi
I drained out some water again to drop the pressure ,its been a couple of days now and the pressure seems ok for now.
I really think that the tankless is leaking into the boiler very slowly now ,raising the pressure slowly because I put in the larger expansion tank.
I called my Installer supplier Eastern Propane and Oil and spoke to them . They said that they would check to see if it would be under warranty ,and get back to me.
Weil McLain web site says residential boilers other than the cast iron boiler are only warrantied for one year.Which means
I will have fix it. The gentleman at the oil company said he has heard of only ONE OTHER BOILER leaking like this in fifteen years. What I am asking here is am I on the right track?
Pex supply has the coil for $199 + $7 shipping.
Everyone I have talked to about this says IT IS VERY RARE
to have the tankless leak internally. But with the boiler feed shut off (its a ball valve) I have no other explanation for this problem.

 

Interesting... it is admittedly rare, but not unheard of.

If you can go without hot water for a few days, and you have the valves, you could always perform the same test that you did with the boiler feed... close the valve feeding the coil and see what happens.

If you have the valving to do so, you could also isolate the coil and pressure test it by itself for a few hours or so...

If you are certain that the feed is shut off 100% and the pressure still climbs, then you are correct that it almost can't be anything else.

Even if the expansion tank were bad, once that feed valve is closed, the pressure shouldn't / wouldn't climb again unless there were another water source into the boiler.

Sounds like you are on the right track, as little used as it might be!

 

Thanks for the confirmation NJ Trooper. Oil Co. called back and said warranty is only one year except the actual boiler. I am convinced, that because I put in the larger expansion tank, is why it lasted all summer before the pressure went up to 30psi again.
I don't think my wife would want to go without hot water for a few days.
I do plan on doing a pressure test on the old tankless after I change it out.
I will report back with my progress

 

If it didnt leak all summer its not the tankless coil. Your expansion tank maybe installed in the wrong location. or if its in a Spiral vent it maybe clogged not letting the tank work properly.

 

I dunno about that Al... think this all the way through before making a conclusion...

First and foremost, the water feed to the boiler was OFF. The ONLY other source of water adding to the system is... a leaking tankless coil.

He lets off pressure by draining water. In a few days, it's leaking again. Where is the water coming from that is building that pressure?

His old tank was a 30, and my guess is that it was waterlogged, and not doing it's job. He installed a 60 size and was OK for a few months, because the extra capacity of the larger tank absorbed the pressure from the slow leak in the tankless.

In this case, the tank location is irrelavent, and the SPIRO vent being clogged would have no bearing either...

Plain and simple, if the system is building pressure, there HAS to be water entering the system. If the boiler feed valve is closed, where else is that water going to come from?

 

If the tankless coil has a hole in it, it wont heal itself for the summer and then open up again when the heat turns on. The pressure would rise all summer too.
If the tank is in a bad location or mounted in a clogged air eliminator when the call for heat raises the temp of the boiler to high limit the pressure will build and release through the relief valve even if the water supply is closed. Hard to tell though without seeing it but every tankless Ive replaced that had a leak in it had a leak all the time. Ive never seen one in thirty five years that had an intermittent leak.

 

Nobody said it was intermittent. What I was tryin' to get across was the fact that at the beginning of the summer, he installed a brand new 60 size expansion tank. And that big ole tank could have absorbed a tiny pinhole leak for quite a while before the relief valve opened. In other words, it was masking the fact that the problem was still there... ever so slowly adding water, raising the pressure... which if he didn't look at the gauge every few days and see that it was a wee bit higher, would have gone un-noticed... until the relief valve spewed again.

But, that said, until we see the results of a pressure test, I won't be convinced that the problem is the tankless coil either...

 

First the old expansion tank WAS NOT WATER LOGGED remember it was only 3 years old.
And I do believe that it is a pinhole leak in the tankless ,and was able to slowly build over the summer because of the LARGER THAN NEEDED expansion tank.
The only way that the pressure could have increased is that water from the tankless is leaking in to the boiler.
Remember I have drained it down twice in the last month now.
Main water feed is STILL OFF
I am waiting delivery of a new coil,expected Oct 19.
I will update

 

I received the new coil yesterday from Pex Supply
Installed it today, it was pretty straightforward install.
I then put 75psi of air to the old coil , put it in a bucket of water
and found that it was leaking on the first inner coil.
It was a small leak ,but that's what I expected ,due to the time it took to build pressure
I took a photo ,but I don't know how to insert it here.
Thanks NJ TROOPER for your help at least you and I BOTH agreed to what it was. And that the larger expansion tank just made it last longer before the pressure built up to 30psi.
thanks again

 

Pete, you want to be VERY careful when using compressed air to pressure test stuff... ESPECIALLY if it suspected to have a flaw.

Compressed air has a LOT of stored latent energy in it... sometimes it go BOOM! and copper schrapnel goes and takes out an eye, or severs an artery.

Pressurizing with water is much preferred, because water can't be compressed and stores MUCH less energy.

But then, how would you have seen bubbles?

Thanks for letting us know what's on tonight's supper table!

By the way, to post pictures, you have to upload them to an off site picture host, like Image hosting, free photo sharing & video sharing at Photobucket ... free account ... then come back here and post a link to the album.

 

I have the same furnace installed 8 years ago. The tankless coil developed a leak while still under warranty. WT 14 replaced under warranty. Now a few years later the tankless coil is leaking again causing the relief valve to leak. I installed 2 of these furnaces at the same time, one in a rental and 1 in my home. The weil McClain it replaced was 30 + years old and never had an issue with the coil. I had a Burnham in the rental that was replaced with the weil McClain. The Burnham also had a leaky coil which precipitated the replacement with the new furnace.

 

Thank you neil for the additional feedback.

This thread is 4 yrs old so it is closed...

Please start new thread...


Thanks...