OWB Sidearm HX causing DHW pressure drop--SOLVED!

[BFL]

Hi all, long time lurker, I am at my wit's end on this issue.

Self installed a CB 6048 last year, this being my 2nd winter with it. My plumbing was set up to go through the sidearm, to the furnace HX, and then back to the boiler. I had a mixing valve on top of the hot water heater to maintain safe temps.

As far as heating the water, it worked great. I ran into several issues last winter where my DHW pressure would drop to almost nothing, or not even supply the upstairs of my house. I had assumed due to the hard water that we have, it was plugging up, so monthly I would remove it, clean the screens, etc. Once the boiler was shut off in the spring and the gas was turned back on to the water heater, we had no further issues.

Lit the boiler yesterday, and once everything was up to temperature the wife went to take a shower and no water pressure. I decided to do away with the mixing valve, and put a manual valve to mix cold water with the hot water. I am still having sporadic hot and cold water pressure. Yea, its wierd.

This only occurs when the OWB is up to temperature. Prior to lighting, I had the circ pump running for a couple weeks to keep the boiler warm as I wasn't ready to light it yet, but we had a couple freezing nights. No issues with water pressure until the OWB was up to temp.

I am really at a loss as to what could be causing this. The sidearm is off the drain of the hot water heater, and the top returns to the hot water outlet at a T approximately 3 inches above the top of the water heater. Again, I have no issues with the water in the heater being hot. Somehow the sidearm, when it is up to temperature, is killing my hot and cold water pressure in the house. The only valves to the hot water heater are both open, there are no leaks.

Tonight I cut the PEX to the sidearm and bypassed the sidearm altogether until I can figure this out. Once I reconnected I went to check water pressure and everything is normal. There are no leaks through the HX, the boiler isn't constantly filling.

Any suggestions or thoughts or ideas would be greatly appreciated. Thanks for your time.

 

[blakey]

BFL, You say the top of your sidearm is plumbed to your hot water outlet. So the water would be trying to circulate via the sidearm and exit the tank to supply dhw to your house at the same time, trying to go both ways in the same pipe. Do you have another port in the top of your tank to use instead? I ended up removing the anode rod to connect the sidearm there. My 2 cents, I'm no plumber.

 

[NSMaple1]

Can you post pics? This doesn't make sense. Even when heating with the sidearm, the dhw flow when water is being used should be through the tank & not the sidearm. So even if the sidearm was somehow blocked solid, it shouldn't affect flows out the taps.

 

[BFL]

 

[BFL]

These are my connections. Don't laugh at the shark bite disaster on top, had to make do with what I could get on short notice lol.

 

[NSMaple1]

It's killing your cold water pressure too? This is a head scratcher. For the whole house?

But I think I see iron piping in your DHW stuff there - which isn't usually good. Black or galvanized. That stuff can grow shut pretty quick sometimes. Should be brass or stainless. Maybe there's something weird going on that the extra heat when heating from wood is somehow closing off more a partially plugged iron fitting up above the top of the sidearm? But that should only affect hot water. I think I would get rid of everything iron & galvanized on all your DHW piping, to start with. If it's not the problem now, it will become one someday, almost guaranteed.

That's the only thing I can think of - otherwise the sidearm plumbing looks OK. I have a shorter one, with the top T'd into the blowoff fitting. If you do re-plumb, I would also put in more ball valves to isolate things for future work.

 

[BFL]

Yep, hot and cold, entire house. The only thing I can think of is when it hot water heater heats up to the higher temp when fed by the boiler, it is pushing pressure back through the cold side and causing some issue with the water softener. That's a heck of a stretch, but it has to be causing trouble with something upstream. That said, the difference in expansion of a tank of 140 degree water vs 180 degree water isn't that much.

There is some black metal piping there, when I tore off the mixing valve I checked and there wasn't much buildup on the inside. I'll add that to my list.

With regards to the plumbing, now that I did it once I know how I should have done it! Next summer I'm tying in my upstairs unit, it will hopefully get done then.

 

[NSMaple1]

Have you followed the heat in the pipes, going both ways from the heater? (Just by feeling the pipes). Wondering if it is working its way backwards to something that isn't made for heat. 180 is pretty hot for a DHW supply, if it does indeed get that hot - there are likely components somewhere that water that hot could mess up. And that downturn through the T into your tank that the hot water has to make after rising through the sidearm might make the heat creep backwards from the bottom. But that's thinking you have a bottom fed tank - but looks like it's a top feed. Which would let the hot creep backwards even easier - maybe. (Circle talk). Anyway, feeling all the pipes to see how far & where the heat is going might find something. And if it's getting to somewhere it shouldn't be, adding a heat trap might help. Or check valve in the right place.

 

[BFL]

The 180 is an assumption. I haven't checked it with a thermometer, but it's awful close to boiler temp judging by feel. I did feel around, I'm not back feeding water into the cold side, the cold pipe coming off the water heater is cold about 4 inches over the water heater.

 

[blakey]

One other think to look at would be the shutoffs which I assume are on the other end of the flex lines we see. The one on the hot line may be affected by the increased temp and if you have pressure balancing faucets you may see both hot and cold affected because there's no hot. I had something similar happen under my kitchen sink, if I opened and closed the shutoff a couple times it would work again. I replaced it and it works fine.

 

[BFL]

Well, I figured out the problem today. The screens, strainers, aerators, and flow restricting orifices on all the showers and sinks were plugged up with very fine sand. So how did the sand get there and why is it when I start the OWB up it happens?

Once the OWB got up to temp, the natural circulation from the sidearm was pulling the cold water from the bottom of the DHW heater, and carrying the sand fines with it that had settled in the DHWH over time. Once we turned on hot water at each of the sinks and showers, it carried that sand to each of them and plugged them up. That explains why it appeared that the hot and cold water were both affected, in reality it was just the outlet that was plugged. During normal operation of the DHWH, the cold water comes into the bottom, the water is heated, and slowly rises, while the sand fines settle out in the bottom. The sidearm being piped off the drain is sucking all the sediment off the bottom and sending it on down the plumbing.

It looks like I'm going to have to get a whole house filter, and flush my DHWH out a little more often. At any rate, just wanted to share what I found.

 

[ChoppyChoppy]

What is a DHWH? Water heater is DWH.

 

[BFL]

Sorry. if DHW is hot water, add an H made more sense to me than swap them around.

 

[NSMaple1]

Huh.

 

[StihlKicking]

DHWH=domestic hot water heater. Switching the W and H in DHW would equal DWH or domestic water heater. Me thinks.....

 

[ChoppyChoppy]

DHWH=domestic hot water heater. Switching the W and H in DHW would equal DWH or domestic water heater. Me thinks.....

I guess. I've never heard it called a hot water heater. It actually a cold water heater.

 

[BFL]

I guess. I've never heard it called a hot water heater. It actually a cold water heater.

Good point. Then again we call them OWBs, and they don't boil anything =)