Radiant Floor Heating System Repair

[59ctd]

I just discovered that my 18 yr old radiant floor heating system is not working and so I am looking for the parts to rebuild it. This is for my 450 sq ft garage/shop. I basically designed this myself back in 2006. Three circuits of 1/2" pex (~485 ft total) in the slab and they feed into two shared headers so it is effectively one closed loop. Cryo-tek antifreeze is the fluid so the heater core won't freeze when the system is off and it is cold outside. The two 3/4" pipes going into the wall are capped off in the attic so they don't do anything. I had originally built it with one 1/25th hp Grundfos pump but found that was not enough flow rate so a 2nd identical pump was put in series and it has worked like that for 18 years. I am not sure if it is the Takagi heater that is the issue or if the impeller blades are gone. Both pumps sound/feel like they are working when it turns on but the heater does not fire. I am going to replace the tankless heater and the pumps. I'd like to get just one bigger pump but I am unsure what size single pump is equivalent to the two 1/25 hp pumps in series. Is it as simple as 2/25 hp or a 1/12 hp single pump? Menards has 1/6 hp three speed pumps that would seem to work fine since I could use whichever speed gives the best flow rate but these 1/6 3 spd pumps are quite spendy. Picture was taken in 2006 when I had just completed the system.

So should I look for 1/12 hp pump, a 1/6 hp 3 spd pump, or just replace them with two 1/25 hp in series like it has always been?

 

[fitter30]

Have you even checked the ph or checked the temperature the what the mix is good for or added inhibitor? Parallel pumps pick up about 80% of gpm head goes up some.
Pump manufacturer has all that info. Propylene glycol has to be at 30% or more for the inhibitors to work correctly. Under 30% prop glycol can turn to garbage in a heart beat. The three valves to the left of the pumps with water hose adaptors would be a great place to back flush.

Pumps - Parallel vs. Serial Arrangement

Adding head and flowrate for pumps arranged in parallel vs. serial.

www.engineeringtoolbox.com

https://oateyassetscdn.azureedge.net/assets/Document/raw_07_BoilerMaintenance_PRODINSTRUCT_001.pdf

 

[59ctd]

The antifreeze was replaced about 4 or 5 years back and I believe I added about 30% water so it is roughly a 70/30 mix. I used no inhibitor - I need to learn more about what that is and how to use it. The PEX tubing says oxygen barrier so what I have been reading is that I can go with a cast iron pump which is cheaper than the bronze choice. I turned on the power to the pumps again just now and it seems like they are both seized so my guess is the pumps are the issue here and maybe not the heater.

The two 1/25 hp pumps here are in series with each other.

 

[Firebrick43]

From the pictures, that does not appear to be a condensing boiler. Why did you not use a primary/secondary loop system?

 

[59ctd]

Mostly because I did not know about a primary/secondary loop system or advantages of that. It is a very simple design.

 

[Packard V8]

Are pumps in series ever good science? Seems the few multiples I see are in parallel.

jack vines

 

[59ctd]

Are pumps in series ever good science? Seems the few multiples I see are in parallel.

jack vines

I doubt it is "good science" BUT adding the 2nd 1/25 hp pump in series was enough to get the fluid to flow enough to trigger the heater on - ~2.1gpm.

 

[American Locomotive]

Before shotgunning thousands of dollars of new pumps and a boiler, why don't you do some basic trouble shooting first?

See if the boiler has any error codes. See if the flow switch is being made. Check or replace the igniter.

Are pumps in series ever good science? Seems the few multiples I see are in parallel.

jack vines

If your issue is not enough head pressure, two pumps in series will more or less double the maximum head pressure at a given flow rate. Normally you'd buy a "two stage" pump that internally has one impeller feeding another, but you can do it with separate pumps too.

 

[59ctd]

Before shotgunning thousands of dollars of new pumps and a boiler, why don't you do some basic trouble shooting first?

See if the boiler has any error codes. See if the flow switch is being made. Check or replace the igniter.

Tankless heater has no codes it just shows there is no flow. Could be the flow sensor. I will start with the pump(s) replacement and if it fires up then good. If not I will put in a new heater they are not really expensive certainly not as much as a boiler.

 

[59ctd]

If your issue is not enough head pressure, two pumps in series will more or less double the maximum head pressure at a given flow rate. Normally you'd buy a "two stage" pump that internally has one impeller feeding another, but you can do it with separate pumps too.

Cool that is how I was kinda thinking how two in series would work - about 2x the force on the fluid. I think I ended up being lucky with the two smaller pump models I happened to buy at the time and it ended up being an alright flowrate ~2.3gpm for the heater. I am looking at the Grundfos UP pump specs now to see what head pressure with the two pumps comes out to ~2.3gpm and if another single pump would be in the same spec range. Thanks

 

[fitter30]

The antifreeze was replaced about 4 or 5 years back and I believe I added about 30% water so it is roughly a 70/30 mix. I used no inhibitor - I need to learn more about what that is and how to use it. The PEX tubing says oxygen barrier so what I have been reading is that I can go with a cast iron pump which is cheaper than the bronze choice. I turned on the power to the pumps again just now and it seems like they are both seized so my guess is the pumps are the issue here and maybe not the heater.

The two 1/25 hp pumps here are in series with each other.

70% glycol is way to much it is killing the efficiency of the pumps and heat transfer. It's harder to pump as the percentage goes up. Any chiller/ boiler glycol has two % charts. One is total protection the other is temperature that it slushes and still protects the equipment.

 

[American Locomotive]

Tankless heater has no codes it just shows there is no flow. Could be the flow sensor. I will start with the pump(s) replacement and if it fires up then good. If not I will put in a new heater they are not really expensive certainly not as much as a boiler.

Shotgunning pumps in there is a waste of money, too, if that's not the problem.

What model is the heater? A new flow switch could be as cheap as $30 if that is the issue.

 

[Dagny]

Hence the need for 2 circulators.

 

[59ctd]

70% glycol is way to much it is killing the efficiency of the pumps and heat transfer. It's harder to pump as the percentage goes up. Any chiller/ boiler glycol has two % charts. One is total protection the other is temperature that it slushes and still protects the equipment.

How did I misread the glycol level requirement? It can often hit -25*F here in Minnesota and the tankless water heater heat exchanger is basically directly exposed to the outside temps with a ~10" exhaust vent.

 

[59ctd]

Shotgunning pumps in there is a waste of money, too, if that's not the problem.

What model is the heater? A new flow switch could be as cheap as $30 if that is the issue.

I think you missed my mention yesterday when I tried powering on the circulator pumps and there was no pump sound just a noticeable hum from the power being applied.

 

[American Locomotive]

I think you missed my mention yesterday when I tried powering on the circulator pumps and there was no pump sound just a noticeable hum from the power being applied.

Are you sure the loop actually has fluid in it? Those cartridge circulators are generally pretty reliable.

 

[fitter30]

How did I misread the glycol level requirement? It can often hit -25*F here in Minnesota and the tankless water heater heat exchanger is basically directly exposed to the outside temps with a ~10" exhaust vent.

Radiate floor systems hold so little volume 450' 1/2" pex hold 4.15 gallons and may be another 2-3 for pump, boiler and piping. 70% is good.

 

[Firebrick43]

Are you sure the loop actually has fluid in it? Those cartridge circulators are generally pretty reliable.

I have heard of quite a few locked up if left setting without being exercised over the summer.

Many of the pump controllers have a "pump exercise" feature now that runs it for a period of time. My calleffi runs the pumps for 30 seconds every 72 hours

 

[fitter30]

Radiate floor systems hold so little volume 450' 1/2" pex hold 4.15 gallons and may be another 2-3 for pump, boiler and piping. 70% is good.

Your good qas long as your covered by burst temp. Measure that ph!!!

 

[Jackfre]

After checking the ph, if you can figure out how to connect it, get a fresh water hose connected to the WH and see if city pressure and good flow fires the unit. This would be simple if you had the tankless iso valves, but it is worth doing anyway. As to the cost effectiveness of a boiler vs another takagi, consider the additional benefits the boilers offer. One you get a circulator built into the boiler, which simplifies your primary secondary piping. As well, you get outdoor reset control which simplifies the wiring and can get the best out of your system. Also they are pretty much all 95% vs your 80 on the water heater.

 

[59ctd]

Last week I found and replaced the 10uF capacitors in the two Grundfos pumps and after that there was no difference - tankless heater did not fire. Friday afternoon I went to try it again powered on the heater, waited a minute and then turned on the pumps and the heater fired up like normal and has been working properly since then. I did order and have here a replacement flow sensor for the old Takagi T-KJr if it stops working again that is most likely the issue I think.

I will be going to Menards tomorrow to get some PH test strips to see how the fluid is.

 

[59ctd]

Here is the test result that I got this morning. To me the ph looks like it is way on the 'OK' end of the range according to the color gauges on the side of the bottle.

 

[59ctd]

How often do you folks check the antifreeze ph?

 

[gerry.pom]

I've used Grunfoss 15-58 pumps for radiant heat in houses much larger than your garage with no issues and some with glycol 30%.
But always with primary/secondary piping arrangement. Some boilers have a built in primary pump others don't. In that case I'll use two 15-58 pumps. Pretty much all boiler manufacturers recommend primary/secondary loops