Have to clean out my water to water heat exchanger

[furjaw]

My Central Boiler 5036 has been running continuously for 5 years and 1 month.
I keep it going all summer just to heat the hot water.
My Taco Model 009-F5 Circulation Pump just died.
The plastic impeller had disintegrated and was mostly missing.
This is the first problem that I have had with the furnace.
It boiled over and I lost about 4” to 5” of water.
I replaced the water and ordered Permanganate so I can test the water to see if I need to add corrosion inhibitor.
I also ordered a gallon of 1650XL Corrosion Inhibitor Plus.
I replaced the cartridge with Cartridge # 009-021RP.
It is working but apparently the flow is obstructed.
I have a water to water heat exchanger.
My guess is that the heat exchanger is plugged up with pieces of plastic from the impeller.

 

[mustash29]

Oh that sucks.

Flat plate braised HX?

As far as small chunks of plastic impeller, that may be a problem. I would disconnect it from the boiler & Pex piping first.

You could try hooking up water & air to back flush it. You would need 2 valves plumbed in to flow it backwards. Hit it with water, shut that off & hit it with air. Alternate that flushing method multiple times. The pressure surges will hopefully dislodge the clogs. It would help if you could catch the debris in a contatainer to see if you are getting anything out. Check your ratings on it to be sure it is rated for a decent amount of pressure. We routinely use this method at my work (power plant) with 100 psi water and 120 psi air to clear clogged drain pipes, drain valves, etc.

If that does not work a local radiator shop may be able to steam clean it for you.

For normal rust scale & sediment removal I would recommend a solution of 10 - 20 % muriatic acid and water. Muriatic is essentially 33% hydrochloric, so use precautions: old clothes, keep if off your hands & out of your eyes, etc. You could also use 100% CLR. You can soak it but it is best to circulate the acid backward through it. It shouldn't take long, 10-20 min maybe. That should clean out any crap.

Sounds like a good time to install a high temp filter or at least a Y strainer to prevent any future issues.

 

[furjaw]

Thanks for the great info!

 

[Bob Rohr]

Thanks for the great info!

Consider adding a dirt separator after you clean or re-install the HX. A separator will remove small particles and trap them in a cylinder out of harms way.

Y-strainers work also, but will reduce flow as they trap particles.

Wonder whey the impeller failed? Usually a dry run condition or cavitation caused wear.

It could be you are air-locked, it would take a lot of plastic particles to plug a HX beyond flow.

 

[thecontrolguy]

Consider adding a dirt separator after you clean or re-install the HX. A separator will remove small particles and trap them in a cylinder out of harms way. Y-strainers work also, but will reduce flow as they trap particles. Wonder whey the impeller failed? Usually a dry run condition or cavitation caused wear.

+1 for the y-strainers. I always find crud in them in old hydronic systems. Especially bits of teflon tape, iron pipe cuttings, little rocks, etc. Have found plastic impellers dissolved in potable water, treated water, and glycol systems so I think heat and cavitation cycles harden and fracture the plastic. If you choose muriatic acid (or sulfamic) do be careful and get something to neutralize it. Also, consider if your treatment chemicals cover yellow metals (brass and copper) with something like tolytriazole.

 

[furjaw]

It turned out that the blockage was not in the flat plate heat exchanger, it was right under the pump between it and the shut-off valve. It was full of pieces of the crumbled plastic impeller.