About 12 years ago (before I learned to never do so), I installed an open system pex radiant heat set-up with two zones and domestic water running off a Takagi tankless. (Don't slam me. I know, I know. Huge mistake.) I did this to gain basement living space and avoid forced air furnace vent space. It worked and I loved it.

Which is to say, it actually worked perfectly for about five years.

I know, a shocker, right? Cause it shouldn't have. Now I know this. The place has a slab zone for 900 square feet and a joist zone at about 1900 square feet, a large kitchen with two sinks and two dishwashers, and two bathrooms. We have a large family of seven, and we are all bathers, so it filled two tubs repeatedly every day. And warmed the house. The slab area was toasty, and the upper joist area was fine.

Then everything changed and I'm not sure why. The system would just go offline, and not heat anything. I replaced the Takagi with a bigger newer model. It would work, then it would stop.

I had to fix it piecemeal because I was putting kids through college and had no spare money.

I narrowed it down to the Takagi filter getting dirty, then the pumps going crazy trying to keep up, then the utility bills skyrocketing because of the higher energy use. Boy do electric pumps burn money.

I tried everything. I replaced the tankless with a bigger newer model again. I replaced the pumps. Nothing worked. The filter just kept getting clogged. We have a guest house that runs off the same city water, but a totally separate tankless unit for domestic use, not radiant. That filter NEVER clogs. I check it. It remains clean as a whistle, even after a year.

Even so, I put a whole house water filter on the main house thing. And it still clogged. I took a plumber's recommendation and separated the tap water from the radiant floors with a heat exchanger and flow switch. This made the problem worse because the pumps were on all the time, 24/7. The little thimble size filter clogs with brown stuff and now some white flakey stuff. I'll upload a picture soon.

At first I was cleaning it monthly to keep things going. Then it was every two weeks, then every week, then every day. I have no sign of leaks or any other problems. Just this strange brown clogging.

A couple months ago, I installed a large Rusco hot water filter (stainless mesh), the kind for hot water systems, and gosh does it really remove gunk from the radiant system. It spins down and is super easy to clean. But still the thimble size filter in the takagi still clogs with brown stuff within a week, though not nearly as bad as before the Rusco. I installed a bigger mesh on the Rusco--which is still about the size of the small filter in the takagi, and I'm down to cleaning the takagi once a week.

I have no money for another couple years to truly fix this thing. I'm happy to live with cleaning it once a week. And I do know I need to fix it. In the meantime, I'm chained to my house weekly, as I open the thimble filter and clean it, once a week.

So here are my questions:

1) Since I have a Rusco large filter on the system, can I live without the tiny thimble size filter on the takagi? I'm already filtering the water anyway, right? I know this voids the warranty, but I already did that with the radiant installation anyway. I'd like to get rid of this little filter now that I have the bigger one, because that would allow me to go out of town for extended periods, and know that the hot water and heat will still work for those left behind. If I have to replace the Takagi, that's $800 every few years, vs. $10,000 for a new system.

2) What on earth could cause gunk like this internally in the system? It wasn't there before I installed a heat exchanger. Could the heat exchange cause that?

3) What is the best solution? I realize a permanent separation is the best option. Should I close the heat zones and install a boiler or a Phoenix hot water tank? Could I then keep my pex piping and avoid a massive remodel? And then go tankless for the domestic tap water?

4) My main goal is to travel (I'm retired) and be able to rent the house out or leave for long periods of time without cleaning this damned *&%** filter.

Thanks for any help you can give me.

I would guess that since you ran open loop it allowed minerals to build up in the radiant tubing and when they hit a point, they started coming loose.

short of filling the system with vinegar, and letting it circulate for a couple days then drain and repeat (don't do this unless a pro comes in and oks it as I have no idea how the rest of the system will take it, but the pex won't mind)

You should be able to install a filter that is fine enough that nothing (except clean water) makes it to the small filter in the tankless. And this pre-filter could be much larger, such that it doesn't need to be cleaned so often.

I agree with krom, too many years of operating with an open system has resulted in buildup. You need a proper flush and to operate wth a closed system using suitable hydronic fluid.

A flush of the entire pex system or just the Takagi?

So if y'all are correct, I have some whitish corrosion on the brass joints that join various stretches of the pex. Nothing can coat Pex, can it? I can flush the whole thing with vinegar, sure. I would guess vinegar is non toxic so I won't worry.

I installed a Rusco Sediment filterwhich removes tons of junk and doesn't clog, because the sediment goes to the bottom. Do y'all think I can get away with using just that, and removing the little Takgai filter? At least for a few weeks so I can have a vacation?

The pumps won't activate the Takagi if the little filter clogs, so if it isn't there, the system won't clog. I would only do this because the Rusco is on it.

By the way, have you checked out the Rusco Filters? I'm impressed. So easy to flush. You just turn a knob and run it for a while, and it's clean. Much easier than shutting everything off and cleaning that little filter.

I did that with the Rusco. So do I have your permission to remove the little filter? ;-) Ha ha. If there is no clogged filter, the system should run fine, because I know that Rusco filter would take months to clog. And it's easy to flush. What issues might I have with microscopic stuff in the Takagi, if I'm flushing it once per month? It's not like those particles would be in there very long.... Thanks. This is super helpful. I can definitely replace this system in five years, but till my kids are out of college, I'm willing to limp along creatively. I rue the day I ever got talked into a sytsem powered by a stupid tankless. Worst decision ever.

Flush the entire system. The buildup in pex is restricting both the flow rate and heat transfer capability.

So as an update... I had the goop and flecks tested and it's simple limescale and black oxidized stuff. Duh. I use a heat exchanger, so it was pretty easy to flush the heatsource side (potable) with vinegar and I removed lots of scale. My local water isn't that hard, but when you heat it and recirculate it constantly as you do with radiant, the heat releases lots of salts and minerals from the water, and voila. I'll be flushing the main radiant lines with a stronger Fernox chemical after Thanksgiving.

The issue is, how to prevent the scale from building up again? I am going to try the electronic water softener gizmo that uses electromagnetic wiring wrapped around the incoming copper water line to change the water so it is softer and doesn't cause scaling. I'm told also that it will release any existing scale over time. If that fails, I'll use a water softener, although I don't like the idea of all those salts and chemicals.

We never needed soft water before, but with lots of heat, we do. I will update this with any news, so that others won't endure the four year hell I've gone through. I sure hope this works.

Exacty right. Once you remove the buildup from the pex, you will see a huge improvement in performance. You really should transtion to a closed loop system that uses good water. Probably the best water is good city water. Second best is distilled water. Well water is usually the worst. While hydronic radiant floor heating systems are efficient and reliable if properly designed and installed, you should still accomplish annual maintenance which might include flushing the system. A simple pH test will indicate when it is time.

electronic water softener gizmo

Don't bother, they don't work.