Adventures in HVAC

It all started so simply. Cold night, cold house, and my office is as far from the wood stove as anything can be and still be in the house. I needed to burn some dead dinosaurs to take the edge off the office before the sun came up and warmed it a bit. But even after the customary minute or two for the warm air to start, I was getting nothing but a cold breeze from the register. Hmmm…

We have a hydro-air system, which means there are air handlers with hot water coils for heat and condenser coils for AC. The hot water coils are fed from the boiler in the basement through long runs of copper pipe. As long as the pipes are intact, there aren’t too many things that can go wrong, and they all come down to problems circulating the hot water.

I took a look at the boiler first. Plenty hot, and the circulator pump for the upstairs zone seemed to be running. Up to the attic, touch the pipes supplying the hot water coil – stone cold. Should have 180° water in them. Water isn’t circulating even though the circulator is fine – that means an air bubble somehow got into the line and has vapor-locked the loop. Cool! Easy fix – all I have to do is bleed the air out.

I exposed the heating coil expecting to find a bleeder valve – yep, there it is. Just a twist with a screwdriver and this thing’ll be fixed in a jiffy – TINK! What? What went “tink”? And why is this water leaking all over the place? And why won’t it stop when I screw the bleeder valve back in? Come to think of it, why won’t the bleeder valve screw back in?

Looks like I’m the one that’s screwed.

Financial ruin goes "TINK"?
Financial ruin goes “TINK”?

The bleeder valve broke when I tried to use it and, naturally, failed with the valve open. What’s worse is that the valve is in no way replaceable – it’s brazed to the copper manifold of the hot water coil. All I could do was replace the whole coil. Groan.

A bunch of phone calls later, I managed to find a replacement coil at a supply house 40 minutes away that would put a $413 hole in my budget. Double groan! Off I drove with five crisp Benjamins in my wallet.

As is my wont, I did a little reading on HVAC and hydronic repairs prior to ripping anything apart. I was particularly worried about draining down the system to remove the old coil – there’s no way to sweat the solder joints apart with all that water in the loop; it acts like a huge heat sink and the joints will never get hot enough to melt the solder. I also worried about recharging the loop: the system has an automatic fill valve to keep the boiler water topped off, but the loops also have propylene glycol in them as an antifreeze since the attic is not conditioned space. I worried that injecting fresh water to top off the loop would dilute the antifreeze and result in the potential for a REALLY expensive freeze-damage repair.

After getting the usual abundantly contradictory advice from the Interwebz, I turned to my dad’s friend, a guy with more than 60 years experience with plumbing and HVAC. He gave me some really valuable pointers, and one excellent suggestion – why not take the coil to a welding shop, have them remove and cover up the wonky bleeder, and then add a tee fitting in the supply line and put a bleeder valve there? Genius!

Not liquid tight - yet.TL;DR – I couldn’t find a welding shop that was willing to help me on a Saturday, so I took matters into my own hands. I went to Home Depot and bought a Bernzomatic brazing torch for $60. Crappy, true, but hot enough to braze with. After burning most of the first oxygen cylinder learning how to get a proper flame and melt a brazing rod, I was able to fill the shroud of the valve with a bronze plug.

Pressure-testing rig.The fill metal was a little on the spongy side, so I figured I should make sure it was going to hold water – no sense in getting the thing installed only to find it’s still leaking. I devised a little rig for pressure testing – a valve, a pressure gauge that’s been sitting around for more than a decade, and some Sharkbite press-fit connectors. I capped the outlet, ran up the pressure to about 60 psi with my compressor, and applied soap solution to my braze. Bubbles galore. More brazing, more testing, lather, rinse, repeat until finally, at about 11:30 at night, it appeared to be holding pressure. I left it pressurized overnight to see if there were any slow leaks, but it held.

IMG_1672I finally got the coil back in place with the new external bleeder valve on Monday morning. After pumping in the coolant I drained down using my transfer pump, I insulated the lines, dressed the wires, and bled the system using the new valve. A few minutes later and the air handler was blowing warm air again, with no leaks.

Lessons learned from this little debacle? First off, a simple twist of a screwdriver could have ended up costing me big time. If I hadn’t known that the lack of heat was likely due to a air bubble in the lines, I would have had to call someone for service. The tech would have realized the system needed to be bled and would have likely broken the valve too. Wouldn’t have been his fault, just like it wasn’t mine, so replacing the coil would have had to happen too. I paid $400 for the coil; with markup, he’d have charged at least $650, plus at least three hours labor. I’d have been surprised to see a bill for less than $800, maybe a $1000.

As it turned out, I paid $60 for a torch and another $20 for oxygen cylinders and brazing rods. Add another $50 for pipe and fittings, plus the $63 I’ll pay for the 15% restocking fee when I return the coil that I didn’t use. So like $200 to make the repair myself. Not too shabby. Plus, at the end of the day, I added another skill – brazing – and I learned a good deal about HVAC and hydronics.

Was it a hassle? Sure. Did it increase my self-sufficiency, and work to free myself from the systems of support? Yep. Would I do it again? You bet.



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