Leaking Tankless Coil?

JoePRI

Sorry if the terms I use aren't correct as I'm just a homeowner and not "in the business".

I have a very old Burnham Jubilee boiler (it has been re-built at least once). It seems to be built like a tank and just keeps on chugging along.

Just under 2 years ago, I had the tankless coil replaced because it had developed a leak. It appears the new coil has also developed a leak as the symptoms are the same as 2 years ago.

Here are the symptoms, please tell me if something else can be the cause.

1. Pressure climbs to 30+psi over a few days when the circulator is running for all 3 zones especially
2. The pressure relief valve opens and vents water to lower the pressure.
3. The system pressure, according to the gauge, is almost always in the high teens or 20+ even when the circulator is off and the system is near its minimum temperature.
4. A few days later, repeat 1&2.

If I remove more water so the pressure is closer to 15 psi (2 story house, boiler in the basement) it isn't long at all until the pressure is back in the higher range.

The steps I've taken so far to isolate the problem.
1. I have closed the ball valve on the boiler water feeder assuming the water make-up pressure regulating valve might be bad and letting in too much water. The system still is venting water even after a month or so. (I know having this ball valve closed is not good in case of a problem. I do check the boiler multiple times a day since I'm working from home and sit close by for about 8 hours a day.)

2. I've "checked" the expansion tank by thumping it and it "sounds" normal (i.e. dull thud on the top, hollow sound on the bottom). My thinking is if the expansion tank was bad I might have this once or twice, but it would soon run out of water and the pressure would no longer hit 30+.

The replacement tankless coil was manufactured by Therma-flow and only had a 1 year warranty. I'm not sure if this is a "fluke" or if 2 years is a normal life for a tankless coil these days. (The previous one was 20+ years old.) I have city water that is not "hard".

Spending another wad of cash on the same piece of equipment if it's going to die in less than 2 years isn't my idea of a good thing. Is there another manufacturer of tankless coils that is better? My service company seems to only use therma-flow.

The problem didn't show up until the heating season started this fall, about November 1.

I'd like to hear anyone's opinion on whether a tankless leak is likely the problem or if it could be something else.

I will have the repair done by a qualified person as the repair is beyond my skill set.

I'm just trying to get some information from those who know. Never hurts to get a second opinion.

Thanks
JoePRI

JUGHNE

Pictures of the coil, piping and valves around it, back up and show several angles....would be helpful.

JoePRI

As requested, sorry I couldn't get better shots as it is sort of in a closet. Let me know if any additional information would be of use.
Hopefully these are helpful

Jamie Hall

The tankless coil may -- or may not -- be the problem.

However, a little troubleshooting will help.

I presume there is an inlet valve to the tankless coil. Turn it off and open a faucet -- and leave it that way through several heating cycles (yeah, I know, no hot water... sorry). What does the boiler pressure do? If it stays nicely constant, that may indicate a leak in the coil. If the pressure cold drops, that may indicate a leak in the coil, too. If there is no change in the coil pressure, the tankless coil is probably not the problem.

Check the expansion tank. There is a little black plastic cover on the bottom. Under that is a Schrader valve, just like the one on a car tire. Using a reliable gauge, check the pressure at that valve when the system is cold. It should be around 12 to 15 psi. If water comes out when you try to check the pressure, the tank is shot, and that could be most of the problem. If no water comes out, but the pressure is low, you can try adding air to it (bicycle pump), but that is a bit iffish (the proper way to do that is to isolated the tank from the system, drain it, and then add air).

Check the pressure reducing valve... again.

JUGHNE

It looks like you can isolate the tankless coil with the valves above it. Blue round handle and blue lever ball valve.
Then drain the coil at the hose bib and leave it open.
Important to leave open if the other 2 valves are closed!
See if boiler pressure rises with this condition, you can run boiler for heating only at this time.

Then with boiler cold/cool and off you can open the cold and hot supply to the coil and carefully watch the pressure gauge for rise.
If the cold incoming to the coil raised the pressure the pressure of the boiler then the water is leaking out of the coil into the boiler water.

JoePRI

Jamie Hall, thanks for your reply. I have checked the Schrader valve at the bottom of the expansion tank to see if there was any water present. There was none.

I have not checked the pressure there because my understanding is that measurment would simply reflect the system pressure unless the tank were removed and drained which I'm not inclined to do.

Is that not correct?

Also, if the expansion tank was the issue, how much water could be expected to purge from the system at high pressure before there was a lack of water in the system? And wouldn't the pressure drop back to a normal range when the temperature dropped and the circulator was off? As time goes by, my system pressure, even at it's coolest temperature and with no circulator running, rises as if water is being added.

I look forward to your comments.

JoePRI

JUGHNE, thanks for your replies.

I could do as you suggest and drain the tankless coil. My hesitation in doing so is, if there is a leak, then my thought was that "boiler water" will be introduced into the potable side of the system. As it is now, the "potable" pressure is greater than or equal to the "boiler" pressure so water would flow from potable to boiler and not vice versa.

Also, if there is a leak, wouldn't I be draining the boiler? Or are we assuming the leak is small enough that it wouldn't matter as long as I don't leave it that way over a long period of time?

Thanks for your insight.

JUGHNE

You should have 20 PSI or less inside the boiler and maybe 50 PSI of house pressure. Yes that difference is keeping the boiler water out of the coil.

With the valves off and the hose bib open you could see boiler water come out if the hole was large enough.
In any case when you wish to put valves back to original positions, you could leave the hose bib open and open the cold water to flush out the coil thru the hose bib.

A better solution for your domestic water heating would be an indirect tank. It has a boiler water coil inside it and heats a tank full of water to be in reserve for use.
I believe that most here believe it a more efficient way to heat domestic water. You do not keep a hot boiler over the summer. It just runs to keep the tank hot. The temp control in the tank tells the boiler when to run.
It could go outside your closet and be used with any future boiler you may get.

You leave the coil in the boiler, assuming the hole is small enough for the boiler water to not pass thru.

Jamie Hall

If the expansion tank were failed and full, one would see the pressure rise -- quite likely to the point where the pressure relief valve failed -- when the system heated. Then, as it cooled off, as soon as the pressure dropped below the pressure regulating valve, that valve would introduce a little more water (not that much, actually -- water isn't all that compressible). And on the next cycle the pressure relief valve would release a little water... and so on.

And you are quite correct: the pressure at the Schrader valve will be the system pressure, if the bladder in the tank is intact and there is an air charge. If you get water, the bladder is shot. If the pressure is very much lower than the system pressure, then the air charge has been lost.