Radiant Zone Failing

OtisRad

I have recently added a radiant zone to my home heating system to warm up a concrete slab. I am having an intermitent issue with the zone’s ability to consistently pull hot water from the boiler. While I can boot the system up, it only runs for a couple of cycles (heats up the slab fully to temperature, then thermostat turns off the pump) and then stops pulling the hot water through the mixing valve. When I purge the zone (flush the cold side and then the hot side the mixing valve, then purge air) the system will pull water for at least one cycle. I thought the issue was air build up, so I installed a supervent on the zone. Nothing changed.

The system is setup as follows -

The main house is heated with a single zone hydronic, force air system. Standard old oil fired boiler set to about 160. This zone has a single pump on the return leg and gate valves on both the supply and return at the boiler. It is functioning 100% fine, both before, after and during the radiant zone installation and operation.

The new radiant zone is Tee-ed off at the boiler on both sides. The hot leg goes to a Honeywell-Sparco AM101-US-1LF mixing valve and then into a Grundfos UPS15-58FC, 3-Speed Circulator Pump, then out to the 250 foot radiant leg and back to a Honeywell-Sparco PV075S Supervent Air Eliminator and then into a Tee which returns to the mixing valve or back to the boiler. I have attached a pic of the leg.

Any thoughts on how to best isolate this problem would be greatly appreciated. Thanks in advance.

Snowmelt

Where's the thermostate? Are you measuring floor temp or air temp. You said the thermostat reaches temp then shuts off? Maybe you need a check valve on the return line at the end of the return for that zone before it connects with the pre-existing return from the rest of the house. You may be getting the cold water working its way back.

OtisRad

Thanks Snowmelt. The stat can measure both air and floor, but I have it set for the floor. Check valve on the return, can't hurt, I can give that spin. Maybe a little back pressure there.

It's bizarre the pump spins, warm water makes it just to beyond the ball valve and won't turn the elbow down to the mixing valve.

Rich_49

Please post a nice clear picture of the entire near boiler piping . The problem will be glaringly obvious I have a suspicion .

OtisRad

Thanks Rich, picture attached.

Snowmelt

I just looked at the boiler pic, is that an indirect water heater, if so I couldn't see the pump, I also couldn't tell what the zone valve on the right was doing?

Mark Eatherton

If my zooming in on the picture is accurate and correct, it looks like the 3 way valve has a C on the top port, and if in fact it does, your valve is installed backwards.

IF the C is on top, flip it 180 degrees, cold purge the radiant zone (and any other zones in need of purging), fire the boiler and turn it loose. You may have damaged the internal element on the mixer depending upon how hot the water from the boiler was. You can also take the knob off of the mixer, bypass the stop, and increase the temperature output of the 3 way, if need be.

BTW, if you don't get air out, it's not an air problem. Stop bleeding. Doing the same thing over and over and getting the same results, but expecting different results is the definition of madness :-)

ME

Rich_49

I also see only one air eliminator and that is on what appears to be the return from the mixed zone and I don't see an expansion tank in any attached photos . I also question the piping arrangement .

Snowmelt

Good call mark I couldn't see the mixer, good call rich I was so focused on piping I didn't notice no expansion tank. Or proper air eliminater, how ever the bypass pipe. I was always told to use a gate valve not a 1/4 turn ball valve.

Rich_49

Butterfly valve would be BEST alternative

Mark Eatherton

I can see where there is a piece of 3/4" soft copper leaving the supply main and going up to a ceiling hung non bladder tank. If he didn't have an expansion tank, his complaints would have been a whole lot different, no?

And sure, the air eliminator on the radiant loop would work better before the pump, but if he does a good job of COLD purging ALL free air out of the system, the MBR will do a good job of getting the dissolved gas out of the fluid. My fear is that with a non cap tank, and the MBR, that he will pull the cushion out of the tank, and be back here complaining about lifting a relief valve and erratic pressures.

I'd suggest he install a bladder diaphragm tank at the boiler, add and air eliminator to the main boiler, switch the pumps to the supply (eventually) and set it all up the way it is supposed to be set up.

Let's see what his response is first though...

ME

Snowmelt

Your right me, would you kinda clean the near boiler piping up. Make it more simplified and direct.

OtisRad

Thanks guys - sorry for the delay in responding.

There is an indirect water tank off the side of the boiler, the pump is at the base of the tank.

There is a non bladder expansion tank in the ceiling as you called it off the soft cooper. I absolutely can and will replace it.

The mixing valve is for sure not upside down - H on top and C on the bottom. Post bleed, the system works tip top. I have taken the mixing valve apart and it appears to be fine.

I was told there is an air eliminator in the boiler, though cannot confirm. I have not had any issues pre-radiant zone install with air.

Not sure why they put the pump on the return for the house zone, it was there when I bought the place. I can move it to the other side.

I think I have done a good job at purging the cold side and then the hot. Your are spot on Mark about the madness aspect of bleeding. Same result every time and it is maddening.

Snowmelt

If the mixing valve is correct, what happens when you by pass the stat and keep the pump running, does the floor stay warm?

OtisRad

I haven't tried that.
If the valve is working and the pump was running continuously sending 120 degree water out, the floor would heat up beyond what I need.

Mark Eatherton

Check for flow from the Grundfos pump. Try QUICKLY closing one of the ball valves in that loop with the pump running. If you can hear a detectable SWOOOooosh as the flow is pinched off, then you have flow. Problem is probably the mixing valve.

If you can't hear a big swoosh, and suspect flow, with the pump running and no heat being introduced into the loop, apply a torch flame to one section of the copper pipe in the loop for 5 seconds. Wait five seconds and CAREFULLY touch the pipe. If it is still hot, flow you've not got. If it's cool,then you're not a fool, because low flow you've got. Possibly partially air bound in the mini tube loops.

What is the sensor for that is monitoring the return water temperature? What is it controlling and what is it set for? Inquiring minds want to know…

ME

Snowmelt

Otis, yea we like to know - try both theory it could be a messed up mixing valve like ME said. But I want to see if the circulater is pumping and keeps sending hot water into the tubes out to the return.

OtisRad

Thanks Mark.

Appreciate the verse and the tip on flow detection using the torch ... Brilliant.

We have flow around the loop for sure. No flow into H. No swoosh when either ball valve is closed, but torch confirms flow out the mixed side through the pump and back to C.

It's the mixing valve, no?

The return sensor isn't controlling anything. It just gives an indication of the heat transfer through the leg. When the system is functioning and it is below freezing outside for days (ground frozen), we send out ~120 and get back ~98.

The room is an old garage which previous owners converted into a den. It is a bit of a dungeon with the block walls and tends to be chilly. I gutted the room and put in a slidding door to open it up. I insulated the floor and over poured a new slab with the radiant loop. It is a nice bright space now but still cold as underneath it is still just an old garage. Anyway, with the stat set at 81 floor temp, the room is a super comfortable 70. I do have two hot air vents from the main house zone in the room (mainly for AC) which only manage 61 when is not heated. The system has been off since the weekend and the slabs at 59, room at 61. The radiant loop is key.

Thanks again.

Gordy

Just out of curiousity are you ramping this slab up, and down? If so you need to pick a set point, and leave it.

OtisRad

No ramping. It'll be a set and forget once the zone functions properly.

Mark Eatherton

"It's the mixing valve, no?"

It's either the mixing valve, or a partially air bound RFH system.

Could be obstruction in the pump, but the loop should still get hot even with just a little flow. Is that an IFC pump?

Was the mixer dis-assmebled and the thermostat removed prior to soldering?

Strange that it works correctly post purge and then no go's on you...

OtisRad

The pump has a removable, integrated check valve.
The mixer is sweat union, so no heat near fitting. I did take it apart and it appears to look fine.

It is strange, driving me nuts. I will see about replacing the mixer.

Thanks

hot_rod

You can remove all the guts from the mixer and try that, if it is a failed valve, this would help eliminate the flow part of the question.

I can't predict what mix temperature will come out, but it will flow plenty with no "insides"

Mark Eatherton

I'd pull the check too. Just to be sure… Pull one item at a time so you don't overwhelm yourself with success :-)

OtisRad

Will do over the weekend and report back.

Thanks!

hot_rod

It's amazing what you can find in circ pump impellers.

Seen 'em plug like this with teflon tape also. What's in your wallet, I mean system

All piping systems that have circ pumps installed in them, really need a strainer or separator installed also. Magnetic protection if ECM pumps, it's cheap and easy addition.

Would you run a car engine without an oil filter?