Flushing a parially blocked DHW line

[homebrewz]

I believe our domestic hot water line is partially plugged. Plenty of pressure on the cold tap, very poor pressure on the hot water tap. The DHW is made by an oil-fired boiler. It also provides the main back-up heat (oil-fired hot water circulated to radiators). I'm pretty handy, but don't know a lot about furnace systems. Is it possible to flush the line out?

The reason why I think its plugged in the first place:
Our tap water source was an old dug well or a pond (depending on the season) pumped into the house by a jet pump. Both sources have pretty hard water. Last year we drilled a well, and ever since, we've had sand and grit coming out of the hot water line, but not the cold tap. My theory is that over years of the other water source, minerals were deposited on the inside of the pipes. Now, the water chemistry has changed somewhat and this stuff is now coming off. I suspect a chunk of it came out and is partially blocking the line. I'm open to other interpretations, but that's the best I can do!

 

[jebatty]

Not an easy task, if even possible. You might try injecting some soap/detergent into the line at the pump end and see if that will loosen up what's there and flush it through. Other chemicals might work, but the issue will be that they probably will loosen more crud and complicate the problem. Hate to suggest it, but you might be looking at installing new hot water lines. I tried everything I could think when I faced a similar problem, and then found a way to get new pipes in without tearing the house apart. Good luck. Happy New Year!

 

[homebrewz]

I was afraid of that. There is a cacophony of pipes in the basement, many are the older galvanized kind. If I can find an inlet somewhere, I'll try flushing it with the cold water line.

 

[Morgan]

If I had galvanized pipes in my house I would rip them all out and replace with PEX (or copper, but for reno work pex is superior), guaranteed these pipes are corroded up bad.............another spot that tends to plug up is the DHW coil in your boiler, if not too bad you could do an acid flush to open it back up, if real bad I would buy a new one, however they are $250-$350 to buy (around here anyway)

To convert to PEX shouldn't be too bad of a job if the basement is unfinished and just one story, if you have any risers up to a second story it can get fun, but really isn't a horrible job, you will have to put a few holes in the walls and ceilings but depending on the job may not be too bad. If you cut neat access holes you can get nice cheap little spring loaded access hatches, cover up the holes until you decide to paint the room, then you can fill in with drywall and paint. When a house was plumbed with galvanized pipe, all pipes and fixtures seem to be fairly central and don't tend to run all over the house, I have done a couple in the past and went fairly well.

 

[DAKSY]

Don't despair. It's not a homeowner fix, but a boiler service tech
will fix you up for probably less than $200. It's the nature of the
beast when you run well water thru a boiler system without in-line
filtration. The minerals cause the ID of the boiler coils to build up
scale deposits that can only be removed by pumping Muriatic Acid
thru the lines. Takes less than an hour, but Muriatic is VERY corrosive
& best left to an trained tech. I hafta get mine done every 5 - 6 years...

 

[woodgeek]

I have a couple lines that are getting pretty closed up---I was thinking of running acid through, but of course I am afraid to.

After much consideration, I've decided that Citric Acid is the way to go....it descales my coffeepot in a jiff, I can buy it by the kilo off the 'net, and it is thoroughly non-toxic.

I was going to try cutting my water at the main, attaching my (slow) tap to a citric acid reservoir, and then siphon the acid back into the pipes by draining the system near the main.

Am I crazy? Please tell me!

One thought---I would not want to do this to a line I get drinking water through--I like some scale on my 50 yo soldered copper pipe.

 

[jebatty]

I didn't mention in my first reply, but I also tried acid. What happened is that additional crud came loose, blocked the pipe solid, I applied pressure up to 100 lbs, but still could not break it free. Acid may work, and then again it might not.

 

[begreen]

Is there a tap where you can check pressure right after the tankless coil? If the pressure is good there, I agree with the suggestion to remove as much galvanized as possible. If it plugs up from rust or scale it is going to fail at some point, hopefully when you are around, but maybe not? We developed a pinhole leak in galvanized in our old house and didn't discover it for a couple days. By then it had made a bit of a mess to clean up.

 

[Highbeam]

Measuring static pressure won't tell you anything in this case, you need to measure flow to evaluate a restricted line. I suspect that when you first open the hot water tap that the water shoots out really quick at first and then tails off to a dribble. That would be expected from a line with lots of restriction in it.

Daksy seems to have some pretty applicable experience here.

 

[homebrewz]

Measuring static pressure won't tell you anything in this case, you need to measure flow to evaluate a restricted line. I suspect that when you first open the hot water tap that the water shoots out really quick at first and then tails off to a dribble. That would be expected from a line with lots of restriction in it.

Daksy seems to have some pretty applicable experience here.

That's exactly what's happening. The pressure builds up slowly behind the closed tap so it comes out quickly when its opened. I rapped on the pipe moderately while running the tap. A couple teaspoons of sediment came out, but no improvement in flow. I suspect it is the coil. I do have some muriatic acid.. its basically HCl. We use it diluted to test for carbonate rocks, but I'm not sure I want to get into flushing it myself. Not even sure what entry point to use.

 

[woodsman23]

I have heard that dry ice or liquid N2 works as it freezes the line and when it thaws it opens the line up.