Very low hot water pressure/volume; flushing coils didn't help

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Theant

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Hello,

Last year we bought a house with an oil boiler, which provides heat via baseboards, and also provides domestic hot water. I do most of my own plumbing work, but I've never worked with a boiler before.

The hot water pressure wasn't great initially, but lately it's gotten really bad. Cold water is great (10 gpm at the hose), but in all the sinks, the hot water stream is about 1/3 or 1/4 the size of the cold water stream.

After reading these forums, I did a coil flush with a gallon of white vinegar and a submersible pump in a bucket. I ran it for an hour. Afterwards, the vinegar was dark brown with a little bit of gunk in it, but nothing major. But the hot water pressure didn't improve at all.

[Edited to add: the coil is in the boiler; I don't have an indirect.]

That was a couple months ago. Last night I did a second flush, this time for 2.5 hours. Same result, no improvement.

Boiler pressure is 20 psi, temperature is around 150F. Other details: our well water is very acidic (pH ~5.2), and also has a lot of iron in it (visibly yellow/brown and smells like iron). For the iron, I installed a stenner pump to inject NeutraSul (peroxide), which solved the problem, but the acidity remains. We're planning to get a more proper solution soon, something like the Pro-OX Iron Filter with calcite blend, to hopefully solve both problems.

What else can I do to troubleshoot/fix the hot water pressure problem?

Thanks,
Anthony
 
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Reach4

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Some system use an "indirect" system where coils heat the potable hot water.
IndirectWaterHeater.png


In others, the potable water goes into coils into the boiler. If that is what you have, I would try your vinegar treatment again and longer. Replenish the vinegar at times. Maybe check the pH of the vinegar water to see if it is time to swap vinegar. You can find two white vinegar gallons for under $5.

0007874204649_A


Besides calcite, it is possible to use another Stenner pump to add soda ash to increase pH. https://stenner.com/applications/ph-control That has the advantage of not increasing hardness. It would be nice if there was a pump that took two pump tubes to meter two solutions in at the same time.

Calcite has the advantage of being intrinsically safer.
 
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Theant

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Thanks for the quick reply, @Reach4. I should have specified -- yes, it's an internal coil in the boiler; I don't have an indirect.

So run the flush for longer than 2.5 hours, really? How long does this typically take? I'll certainly be happy if the problem can be fixed with just more time and more vinegar!

Is there a way to tell when it's "clean"? I guess when the vinegar remains clear instead of turning dark brown?

For the acidity problem, I have considered the second stenner pump with soda ash. It would be a lot cheaper: ~$350 for the pump, vs ~$1300 for the Pro-OX Iron Filter system & calcite. But with a pair of stenner pumps, and now two buckets of solutions that need to be refilled pretty often (1-2x/month for the peroxide anyway), it's starting to seem kludgy -- a single tank with ~annual maintenance seems easier and more professional.
 

Reach4

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So run the flush for longer than 2.5 hours, really? How long does this typically take? I'll certainly be happy if the problem can be fixed with just more time and more vinegar!

Is there a way to tell when it's "clean"? I guess when the vinegar remains clear instead of turning dark brown?
I have no relevant experience. I would think not turning dark brown would be one criterion. Another would be the pH would stay low. I would think under 3, but 3.5 would be more relaxed.

There are other acid solutions made for the purpose that may have phosphoric acid or other. Vinegar is readily available and probably safer than some other choices. If a few more gallons of vinegar pumping overnight don't do it, maybe investigate something more active.

How do you measure pH now? Cheap pH meter with pH 4 buffer solution for calibration seems pretty good for this. Cheaper than good pH strips probably. I think one packet mixed with 250 ml (250 grams, 8.45 ounces) of distilled water makes the calibration buffer solution. Save some glass jars with lid for the solutions. The meter usually comes with 3 packets for different pH. You use the one closest to what you are measuring to calibrate.

Store the meter, cap down, with some buffer solution in the cap. Recalibrate each time you use the device.
 
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Fitter30

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5% vinegar has a ph 2.5 weaker the solution the higher ph. Don't know if beer or wine making stores carry litmus paper 4ph.
 

Dana

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What fitter20 said- use a higher concentration type vinegar before giving up on the internal coil.

If the coil is too limed up to be restored to reasonable service, don't replace it- invest the coil money in either an indirect (which would offer a LOT of hot water), or a heat pump/hybrid water heater, which would have a lower operating cost, and helps dehumidify the basement/boiler room in summer.

With a heat pump water heater you can turn the boiler off for the summer, which is when it's efficiency bottoms out. If located in the same area as the boiler, the heat pump water heater "harvests" the standby losses from the boiler during the heating season. With no internal coil the idling temp of the boiler can usually be safely dropped to 140F, which reduces those jacket losses too. In most homes the boiler room is the warmest place in the house all winter if the idling temp is 150F or higher. (Is the boiler room or basement foundation walls insulated on the exterior walls?)
 

JohnCT

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Hello,

Last year we bought a house with an oil boiler, which provides heat via baseboards, and also provides domestic hot water. I do most of my own plumbing work, but I've never worked with a boiler before.

The hot water pressure wasn't great initially, but lately it's gotten really bad. Cold water is great (10 gpm at the hose), but in all the sinks, the hot water stream is about 1/3 or 1/4 the size of the cold water stream.

After reading these forums, I did a coil flush with a gallon of white vinegar and a submersible pump in a bucket. I ran it for an hour. Afterwards, the vinegar was dark brown with a little bit of gunk in it, but nothing major. But the hot water pressure didn't improve at all.

[Edited to add: the coil is in the boiler; I don't have an indirect.]

That was a couple months ago. Last night I did a second flush, this time for 2.5 hours. Same result, no improvement.

Other details: our well water is very acidic (pH ~5.2), and also has a lot of iron in it (visibly yellow/brown and smells like iron).


I had a similar problem with my DHW coil. The coil was connected with two unions, so I disconnected them and I ran a 50/50 solution of CLR through the coil, and the thing foamed like you wouldn't believe. I did not run a circulation pump like you did (mistake I think). Unfortunately, the damned coil plugged completely and I couldn't get anything through it after that. It's like the CLR dissolved all the internal deposits and turned it into epoxy. I bought a new coil and that fixed that...

Regarding the pH, mine averaged between 6.2 and 6.5. My house was built in 1993 and required a complete repipe. I added a Calcite tank and my pH is now 7.0 to 7.2. My understanding though is that Calcite itself may not move the pH more than one point, so the 5.2 may be beyond the limit of Calcite alone.

John
 

Theant

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OK, I'm running another flush now. Still using plain 5% white vinegar because my high-strength 45% stuff won't arrive until tomorrow. But 1 hour into this flush, the vinegar is definitely less dark brown than it was a few days ago -- it's more a translucent brown now. The vinegar's pH was initially 2.2, and now it's 2.5, so still pretty acidic. I'll let it run another hour then test again, and probably repeat this tomorrow night.

One interesting note: after killing the power and isolating the coil, I ran a few gallons of cold water through it, to cool it down a bit before starting, because last time my submersible pump overheated. And the water was really gushing out (this was from the normal cold water input, not my pump). Yet at the utility sink 10 feet away, it's barely a trickle. Maybe my problem is an obstructed pipe after the boiler, rather than in it?

Re: calcite, Clean Water Store offers plain calcite, which they say is good down to a pH of 6, and then a calcite blend, which is good down to 5. So I'll be trying the latter.
 

Theant

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Well 2.5 hours later, the dirty vinegar pH was 2.6. I stopped it at that point, and upon dumping it from the orange bucket into the white utility sink, I saw it wasn't actually brown, but gray, with a blue-green tint. So presumably I'm getting down to some copper now, which seems like progress.

But the problem remains: the hot water pressure is terrible. The stream is still only about 1/4 the size of the cold water stream, in every sink.
 

Reach4

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How about recirculating the flow through one of those sinks via a hose? Then you would be cleaning that one path. If successful, expand to another path.

You could tap in at the stop valve connections. There are also aerator-thread adapters.

I am thinking a water softener would be good for you. You would prevent future deposits, and even slowly remove some existing deposits.
 

Fitter30

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How is the flow through the coil while pumping vinegar? The valves including cold water supply to the hot water when opening and closing to they feel the same and count the turns from open to close. Then cut the line in a couple of spots for inspection.
 

Dana

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One interesting note: after killing the power and isolating the coil, I ran a few gallons of cold water through it, to cool it down a bit before starting, because last time my submersible pump overheated. And the water was really gushing out (this was from the normal cold water input, not my pump). Yet at the utility sink 10 feet away, it's barely a trickle. Maybe my problem is an obstructed pipe after the boiler, rather than in it?

Scale thrown off a limed-up tankless coil can clog taps with aerators with grit in the aerator. Pipes down stream of the hot water feed can sometimes lime up too, especially if it's un-tempered hot water at full temperature.
 

Theant

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How about recirculating the flow through one of those sinks via a hose?

Meaning use the submersible pump in a bucket of vinegar like I've been doing, except expand the loop to include a sink? That seems worth trying.

We do have a softener. It seems to run normally, it backwashes, etc, but the water is never very soft. I think I've read that they don't work very well on acidic water?

How is the flow through the coil while pumping vinegar? The valves including cold water supply to the hot water when opening and closing to they feel the same

The flow is great while pumping vinegar. Valves are all quarter-turn type, and all turn fine, all feel about the same.

Scale thrown off a limed-up tankless coil can clog taps with aerators with grit in the aerator. Pipes down stream of the hot water feed can sometimes lime up too, especially if it's un-tempered hot water at full temperature.

The cold water runs great in the sinks so it's not the aerators. Pipes limed up seems like a possibility. We do have an anti-scald valve (thermostatic mixer) after the boiler so it's not quite full temperature there. (And I put a bypass around the anti-scald valve, to verify that the valve isn't the problem -- no difference in the terrible hot water pressure with/without the bypass turned on.)
 

Arseniy M

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I have a very similar setup with oil fired boiler and internal coil for DHW. Only difference is -- no well. Quick suggestion though. Have you tested pressure before the inlet to the coil? I'm sure there is a tee (or a series of tees) leading up to that inlet. For me, there's a tee just before the inlet to the coil and one end goes into the coil and the other end goes into a backflow preventer, pressure reducing valve and into the return of the heating side of the boiler. Not ideal way to have it setup, but it works. So yes, seems to me that you are a DIY kind of guy, think of a way to test pressure before the inlet.
 

Theant

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Well this turned out to be a gunked-up filter, combined with user error. When I had my thermostatic mixer valve bypassed, the pressure in my utility sink was still low -- but I had forgotten that I'd turned down a valve just before that sink, because it shares its pipes with the washer, and when the washer runs, the whole house loses pressure. When I remembered that, and opened that valve, I got full pressure through the bypass.

That left the thermostatic mixing valve. I removed it and discovered (re-discovered...) that it has metal screens on its inlets, and sure enough, the one on the hot side was all gunked up with iron. Cleaning that filter solved the problem. I've been doing that every month or two and it's kept the pressure good.

Thanks for all your replies.
 
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