Boiler working - feed lines hot to floor but floor not heating

Nanook

I have not been able to find a discussion which matches this issue. The 6 zone electric boiler (Electro-boiler, model EB-C-31) is working well (22 psi and 170 degrees). The hot water tank loop is heating the water tank with no problems. There is a heating loop in the forced air system (set up for air conditioning). Fortunately, the forced air loop is hot. We live in northern MN and we have been using this loop to keep warm. The pipes are hot to the four zone lines entering the floor. The return lines remain cold after over 24 hours of calling for heat.

We have replaced line pumps and mixing values. The lines have been flushed with the external hose and pump. The lines flow well with the external hose and pump. Any air in the line has been pushed out. The thermostats are working and match the forced air temp but never reaches the in-floor set point. The controler turns on/off the pumps when the thermostat is adjusted. The air separator has been inspected and cleaned.

The system was installed 18 years and has always heated the floors without an issue. No recent changes to the piping. Those same guys have been trying to solve the problem. But after four days of working on the system they appear to be stumped. Any suggestions are greatly appreciated.

Ironman

Lack of flow is usually caused by two things:

1. Air binding
2. A problem with the circulator(s).

This assumes that the piping and controls are correct.

Since you state that it’s worked for 18 years and that the circulators have been replaced, and that’s it’s been purged of air, there really isn’t much more general advice that I can think of.

How about posting some pics of the system?

Intplm.

@Nanook Here's a thought. Because it has worked well in the past what was the reasoning to change any of the parts? Was it before or after you discovered the cold returns?

I'm asking because the only thing left is that you might have lost the insulation under the slab. How? I have no idea.

Is the direction of the circs correct? has the slab been undermined losing its insulation?

hot_rod

Plugged mixing valves is another possibility. Depending on the brand and model, some have fine mesh strainers at the H&C port.

Look for any other y strainers, and sometimes plugged air purgers.

It sounds like flow has gradually dropped off?

GroundUp

Can you share a couple photos? Also, which part of northern MN? I may be able to assist you with this either remotely or on site, if I can see some photos to help troubleshoot.

Nanook

Thank you for you comments. It does not make sense for the system to not heat the floor. So, I really appreciate your help with attempting to solve this problem.

I included three photos at the end of the message. The four lines to the right of the control panel goes to the force air system and the hot water tank. Those lines are working correctly. The larger boiler loop line is hot. The pipes are hot past each mixing value, pump and to the tubing going to each zone when the thermostat is activated.

Each of you asked good questions.

We replaced the parts after we found the four zones were not heating the floor.

The slab is stable and there has been no shifting of the ground or house. We have the water supply line off and we are not losing water. We did do a pressure check of the lines and pressure was maintained.

The circs are flowing the correct direction. Several mixing values were replaced. As we turn the mix valves the temperature will change temps at the valve discharge. It gives us the impression there is a flow to the zones but all returns are cold. Is there a way to measure the flow from the zones based on what you see in the photos?

The air purger was inspected, cleaned and reinstalled. As with the pumps and mixing valves the purger was not gunked up.

A couple other items the might be helpful. 1) The boiler pressure gauge appears to be working correctly because we did pop the relief valve when we went a few pounds higher (I think 30 psi). 2) The magnet was install after doing other items. We did find the manufacturer placed a collar in the inlet line which was found as we wracked our brains on the issue. We thought that was the problem but removing the collar (not supposed to be inside the line) did not resolve the problem. 3) One of the two boiler circuit breaker had tripped a few days ago. This happen one other time this season.

We live along the North Shore outside of Duluth MN.

We are stumped with solving the problem. Again, thank you for your help.

109A_5

Hello Nanook,

Are these valves ? If so, and if you have not already tried, maybe shut them all off except one on one zone and see if you can get one loop to work at a time. If you can get each loop to work individually add more and see what happens. Maybe just experiment on one zone at a time.

GroundUp

Those Taco mixing valves have an extremely fine screen in them, which could very well be plugged with debris. If it's not airbound and the circulator is running, I'd bet my next paycheck that the mixing valve is either stuck or has a plugged screen.

Nanook

109A_5, I had the same thoughts yesterday and I did exactly what you suggested. I turned four off and left the right tube open. Then, I set the forced air at 69 and set the floor thermostat at 74. Immediately I could feel hot water flowing into the tube. I did this with all lines with the same result of hot water. Then, I opened all lines to run during the night.

We have slate floors in that zone so we can feel the warm floors if it is happening. After several hours last night the area where the zone starts the floor was warm (maybe 3 sq ft). This morning the room is at 69 (forced air set point). The warm area on the floor is maybe 8 sq ft. The return lines are maybe 2 - 3 degrees warmer than last night. I understand the concrete is a huge heat sink but in the past the floor heated much faster and definitely would have been at 74 this morning.

Groundup, we did replace the mixing valve on second zone from the right. We have not replaced the first zone from the right which is the zone I referred to in the comments to 109A_5. All of the mixing valves are responding correctly when opened and closed. I just set the zone 2 thermostat at 74. The line after the pump entering the floor was immediately hot. I will leave the zone 2 floor thermostat at 74 today (we had done this recently with no success). I will talk to the tech about replacing the zone 1 mixing value (with the holidays I am not sure when he will get here). Although, the temp after the pump is hot it could be the flow is restricted and not enough to heat the floor. But, that problem would need to be true for all four zones (including zone 2 with the new mixer).

The rate flow on the zone 1 pump (new) is 8.5 gpm. I just checked the flow (5 gallon pail, 30 sec) the the flow rate is roughly 3 gpm. (I didn't run longer because I need to keep the antifreeze in the system.) Is that flow rate expected due to line loss or does this help ID the problem? I could try running zone 1 with three lines instead of all five to increase the flow in those lines from 0.6 to 1.0 gpm (if the calc works that way).

Again, thank you for the help. It is great to have extra experienced eyes working on this.

Merry Christmas.

hot_rod

Was the main dirt filter disassembled and cleaned, the black canister?

Here is a pic of the screen and check valve that may be on the H&C ports of those mixers. If those are in place , remove both the checks and screens. Those are mainly for domestic water protection.

That black filter will provide plenty of dirt and debris protection for your components.

Screenshot 2024-12-21 at 8.53.46 AM.png

Screenshot 2024-12-21 at 8.45.07 AM.png

GroundUp

Dumping fluid out of a pressurized system has no bearing on actual system flow rate, FYI. You could have turned the pump completely off and had the same result. I'm still leaning toward a plugged screen, which would take 30 seconds for you to check on your own if you're comfortable opening the system up

Nanook

Hot_rod and GroundUp, I agree it feels like it is a restricted flow issue. All four zones have the same issue of not heating the floor. The mixing valve when adjusted and the pumps for each zone appear to work well. The hot water tank and the forced air system (no mixing valves) are working very well and normal (upper right in photos).

The black canister is actually a magnet to separate iron (NaviClear by Navview). This canister was installed after we started having problems with the heating of the floors. No filters or restriction in the canister.

Update on zone 1 (first pump on right side of pic). New pump has been installed. After 48 hours the room temp is 69 (matches the forced air temp of 69) while the thermostat set point for the in-floor is 74. The feed line from the mixing valve to pump to tubes are hot. The return line is about 8 degrees warmer. The floor is warmer but not enough to increase room temp.

Update on zone 2 (second pump in on the right side of pic). A new mixing valve has been installed. 24 hours ago, the in-floor thermostat was increased to 74. The room temp is 65 which is no change (forced air temp controlled is in zone 1 area). The feed line from the mixing valve to pump to tubes are hot. The return line temp has not changed.

Being the zone with the new mixing valve and the other zone with a new pump are not improving the situation and all four zones have the same problem, does this suggest the issue is with the boiler loop? Is there something in the boiler that could be obstructing the flow? The air separator has been inspected and is good.

It is probably better to have the tech check and replace all mixing valves (minus screens) when he returns. I am a novice with this, so thanks for setting me straight about the gpm comment.

Nanook