Tankless Coil Dry Flushing

julianne_lynne

Hi everyone! I have a Slant Fin oil fired hw boiler with tankless coil. I’ve been having issues with hot water run out and reduced pressure for about 3 years now (boilers only 5 years old). Since Slant Fin parts are becoming scarce, I picked up a replacement coil while I still could but was hoping to do an acid wash to the current coil to get the most life out of it before using the new.

In reading about acid wash’s and the damage it can cause to the copper pipe, I’m wondering if there is a safer way that I could flush/clean it when dry? i.e. I would take out the existing coil and install the brand new replacement then allow the old one to dry out for awhile and then be able to clean it and keep it as my back up

Just curious to hear everyone’s opinions!
thanks in advance

STEVEusaPA

Never heard of slant fin parts becoming scarce. Coils are easy to get.
That’s rather soon for a tankless coil. What kind of water do you have?
Do you have a mixing valve? If so, I’d start there.
I’d take temperature readings in, out and mix, to make sure you are getting the right temperature to the fixture. If you do, then I’d check point of use mixing valves, and shower head flow rates.
Do you have enough water in the boiler?
There’s a few you tube videos on coil flushing.

Jamie Hall

If you don't let the acid sit in there forever, and if you use a reasonable acid -- citric or acetic for instance, you'll not have a problem. Just flush it with clear water well.

Mad Dog_2

You could also "bounce" the coil with kinetic shock waves.  Mad 🐕 Dog

EdTheHeaterMan

I used to use the product called "Sizzle" which was a very strong acid. https://www.supplyhouse.com/Hercules-20305-HERCULES-1-Quart-Sizzle-Drain-Waste-System-Cleaner That worked well but had strong warning to make sure all the acid was flushed out before recommissioning the coil for DHW use. It even came with PH test kit. More recently, after the introduction of Tankless Gas Water Heaters, I started to use the pump kit with the vinegar based chemicals. In place of the 5 minute of Sulfuric Acid, I now prefer the 30 minute of Vinegar pumping thru the coil. I would hook up the pump and start the mild chemical flush, then continue with the rest of the tune up on the burners. I had a flat rate price for the flush only and a lower price flat rate for the flush during maintenance. (Economy of scale, getting 2 jobs done at the same time) it was like getting paid time and a half and the job was safer for the customers and the pipes.

https://www.supplyhouse.com/Rectorseal-68708-Calci-Free-Tankless-Water-Heater-Flush
https://www.supplyhouse.com/Rectorseal-68711-Calci-Free-Tankless-Water-Heater-Flush-Kit

EBEBRATT-Ed

@julianne_lynne

Coils are available elsewhere you don't have to get them from slant fin. Everhott is one supplier

psb75

Heated vinegar works even better than cold vinegar when flushing. Use vinegar at full strength. You could also use diluted Sizzle®.

julianne_lynne

EBEBRATT-Ed said:

@julianne_lynne Coils are available elsewhere you don't have to get them from slant fin. Everhott is one supplier

Yes I purchased from parts4heating but there weren’t many available overall. Slant fin discontinued them almost a year ago and since they aren’t making boilers anymore and have sold off most of the company I figured stock is likely going to continue decreasing. (Assuming though- could be wrong!) 

julianne_lynne

@STEVEusaPA I should have mentioned I have either a deteriorating well casing or rotting well pump so theres a lot of rust flakes at times. Just installed a spin down and sediment filter though (no change to hot water issues though). Yes we have a mixing valve. I kind of just assumed because of the pressure reduction that it was a clogged up coil.
At the sink; hot water flows strong and hot but if I keep it on hot for awhile, eventually the pressure reduces to about half and the water turns to Luke warm until the boiler kicks back on then 30 seconds later pressure is back up and water is hot. And showers suck in the winter! The shower head has a high flow rate so unless you keep it at a steady warm temperature, you’re eventually taking a cold shower for a minute until boiler kicks back on.

EBEBRATT-Ed

@julianne_lynne

TFI Everhot has tankless coils for 50 year old boiler or older. They may not be off the shelf but they have measurements for all boiler so they can make one.

One thing you should do is make you shower head(s) lower flow. Tankless heaters are not known for their hot water capacity. They are at best good for 2 people. Careful use (not running hot water at the same time in multiple locations will help as will slowing down the flow.