Help with floor heat

[slash007]

My floor heater keeps tripping the limit switch on the thermostat if I turn it up at all, and I was wondering if anyone had suggestions of what to look for. I am not very familiar with it but know the first year I owned the wash, it operated flawlessly and all heated areas were snow/ice free the whole winter. The past year and this year as well, I kept finding that it would be off and the limit switch on the built in aquastat would be tripped. I lowered the knob on the gas valve (flow? temperature?) and now it stays on, but it is almost pointless as it is not warm enough. I think the temp is around 32 degrees. I really need to up the temp by a couple of degrees in order for it to be effective, but that trips the switch. Any ideas on what might cause that?

View attachment 727

 

[cantbreak80]

The “Automatic” high limit stat turns off the gas valve when the set-point is achieved. The “Manual” high limit stat is there as a backup…to prevent overheating in the event of an automatic high limit failure. When the manual stat trips, it could be an indication of too little flow through the boiler, among other things.

Assuming this is a modulating Raypak boiler, first thing to check is the flow switch. Is it operational, or has it been by-passed?

Second, adjust the Manual High limit UP to 150 degrees and lower the Automatic High limit to 120 degrees. Then, adjust the gas valve back up to it's prior setting.

Now, when the boiler fires, it should come up to full flame and slowly modulate down as the return temperature increases.

 

[slash007]

The “Automatic” high limit stat turns off the gas valve when the set-point is achieved. The “Manual” high limit stat is there as a backup…to prevent overheating in the event of an automatic high limit failure. When the manual stat trips, it could be an indication of too little flow through the boiler, among other things.

Assuming this is a modulating Raypak boiler, first thing to check is the flow switch. Is it operational, or has it been by-passed?

Second, adjust the Manual High limit UP to 150 degrees and lower the Automatic High limit to 120 degrees. Then, adjust the gas valve back up to it's prior setting.

Now, when the boiler fires, it should come up to full flame and slowly modulate down as the return temperature increases.

It is a Raypak boiler. I had no idea what those do, so I was afraid to mess with them. I appreciate your input and will try those tonight. Hopefully it is still on tomorrow. It's going to be -15 here on Thursday, so I really need the loop in my trough to stay on.

Thanks!

 

[slash007]

I made the changes you suggested and turned the know on the gas valve up to six. So far it is not tripping the limit, but the flame is turning on and off very often. Is that normal and ok? I noticed the temp goes up to about 34 degrees and then the flame turns off. And then after about a minute or so, it turns on again.

View attachment 728

 

[cantbreak80]

slash,
First...the design temp for most floor heat systems is usually +10 degrees. You should not expect ice free performance at ambient temps below the design temp. That's also why your home's heating system has trouble keeping up with the unusually cold nights.

As for the gas valve short cycling...that's not good. Commonly, those high limit switches are used only as overheating protection. The control that turns the system on is a Slabstat...a remote-bulb thermostat that's mounted on the wall, with the sensor located in a conduit buried in the concrete.

So what's happening? The boiler is "bouncing off the Hi Limit". The burner turns on...the temp goes up...automatic High Limit is achieved...gas valve closes.
Then, the circulator continues to run...pushing cold glycol into the boiler which cools the HL sensor and "whomp"...the burner fires and the process repeats. You're right, it's not supposed to work like that.

Things to check:
Is the glycol level visible in the sight glass? It should be at least at the red line on the glass. If not, DO NOT open the tank until you've allowed the system to cool...there may be significant pressure on the system and you can be seriously injured by hot-steamy glycol suddenly released.

Look for the by-pass valve between the boiler's inlet and outlet piping. It should not be fully open, or fully closed. If you're unsure, close it fully with the system running...the boiler might make some odd sounds. When that occurs, slowly open the by-pass until the noise goes away.

Did you inspect the flow switch? Note...There's 120 volts under that cover...Danger...don't get shocked! There should be two wires, connected to two different terminals on the switch. If both wires are connected to the same terminal, the switch has been overridden. The flow switch is another safety device to prevent boiler operation in the event of low liquid level or lack of circulation. If the switch has been by-passed, there's a possibility that the circulator's impeller is worn out (not uncommon on Raypak's header mounted pumps). If the circulator is installed on the pipeworks, the worn impeller is less likely but still possible.

Start there and let's see how to progress.

 

[slash007]

First off, thank you very much for your responses. They are very helpful.

I checked the flow switch and it is installed and working properly. It actually has a test switch on the side and when activated, it shuts off the flow and the boiler, so I know it works. The bypass valve is not fully open or closed, so that isn't the issue either. The glycol level is low though. Here is a picture: View attachment 729

Will a low level cause it to exhibit those symptoms? I left it as is for now. Will it short cycling cause an issue in the short term, or do I need to drive back over there and make a change?

 

[cantbreak80]

slash,
Short term, this should not be an issue. I'd be concerned about the frozen trough plumbing, unless that loop is staying warm. Otherwise, it may be in you best interest to close the car wash and purge all the bay supply until the sub-zero conditions pass.

These systems are typically non-pressurized...except for the pressure created by heating the glycol. You can't always trust the pressure gauge on the expansion/fill tank, so it's always best to be safe before removing the fill plug....when the system is cooled. The level is not sufficiently low to cause the problem you're experiencing, but visual inspection of the fluid movement inside the tank will aid in diagnosis...and the only way to do that is to remove the fill plug.

I hesitate to suggest removing the plug while the system is operating and hot...again, you can be seriously injured.

 

[I.B. Washincars]

A simple fix for the trough heat would be to just feed HOT water to your weep system. I don't understand all these trough heating systems that people install when they already have one plumbed up.

 

[slash007]

I.B., I do weep hot water at my other wash that doesn't have trough heat and it works good. This one had the floor heat already plumbed with a line in the trough and that has really helped, so no reason to weep hot water there yet.

cantbreak,
with the way it is currently operating, is it serving it's purpose and the lines are staying warm? The boiler runs for about 2.5 minutes then is off for 35 seconds or so. If I look in the glycol tank, what am I looking for exactly?

Thanks.

 

[Earl Weiss]

A simple fix for the trough heat would be to just feed HOT water to your weep system. I don't understand all these trough heating systems that people install when they already have one plumbed up.

Trough heat is closed loop and can run Hotter than weep without the waste. Weep flow is much less, especialy with the weep mizer so it provides some benefit but not wnough. (Todays predicted high +11, Tommorrows +3)

 

[cantbreak80]

If I look in the glycol tank, what am I looking for exactly?

slash,
So, why is your boiler bouncing off the high limit? There are 4 or 5 possibilities:

Low water flow
Temperature setting too low
Interrupted pump operation
Modulating control set too high
Excessive by-pass flow

Low water flow is possibly due to an eroded circulator impeller. This is why I suggest observing the velocity of the glycol inside the tank. If the flow from the boiler is significantly reduced, the glycol solution is spending too much time inside the boiler and is getting super-heated. Since the HL probe is located in the boiler’s outlet header, this high temperature hits the probe and the burner is extinguished. A few minutes later, the continuous introduction of cooler glycol lowers the header temperature, the HL switch closes and the burner re-fires.

If the Automatic High Limit is set too low, the boiler’s heating capability quickly reaches that setting and the burner is turned off. Start with a HL setting of 150F…and adjust the MANUAL HL to 170 to 180F. (This will aid in preventing heat soak temperature rise from tripping the red button.)

Interrupted pump operation is unlikely…or you would have reported that, right?

Modulating control set too high. Since this has been recently adjusted, this might be a contributing factor. The standard factory setting is #5 (approx. 143F)…each value on the dial is approximately 6.5 degrees +/-. 143F is good because flue condensation occurs at temps below about 140.

Excessive by-pass flow. The idea here is to temper the boiler’s inlet, reducing warm up time for the returning glycol and preventing thermal shock and flue gas condensation. But, too much by-pass volume will quickly bring the Delta T to zero…the boiler heats the already hot glycol and the set-point of the HL is quickly satisfied.

So, if the issue with the boiler is a recent change from normal, and nothing has been tinkered with, low water flow would be my first suspicion. However, if the by-pass has been “tweaked” open, that alone could be the culprit. Finally, simply adjusting the gas valve and HL settings to “balance the operation” may be all that’s necessary to stop the short cycling.

Therefore, the BIG question…did the boiler operate “normally” before you began experiencing the Manual HL reset issue? If so, what changed that caused the HL to trip.

Or, has the boiler always short cycled? If so, it was not properly adjusted during initial start-up.

 

[cantbreak80]

A simple fix for the trough heat would be to just feed HOT water to your weep system. I don't understand all these trough heating systems that people install when they already have one plumbed up.

I.B.,
Good solution but, not all facilities are equipped with "pressurized" hot water.

 

[I.B. Washincars]

I.B.,
Good solution but, not all facilities are equipped with "pressurized" hot water.

I can't remember ever seeing a wash with no water heater at all. I guess there may be some down south, but I don't see them needing to heat a trough.

 

[2Biz]

I weep un-softened "Cold Water". I don't see a need to weep "Hot" softened water for more than one reason. Although, I guess my weep is hot by the time it makes it through the trough. I have Raychem heat tape and a zone from the floor heat running through it. It stays a cozy 110° in there. So In a sense, you could say I weep warm water!

 

[slash007]

This morning the floor heat was still on and working, but still short cycling. That is with the dial on 6 and the auto limit on 120, manual 150. I changed the auto limit to 155 and the manual to 165. I would have set the manual higher, but it seemed to have a stopper that prevented it from going any higher. I'm sure I could have removed it, but figured maybe it was there for a reason. I left the dial on six. It ran for about an hour or so and then tripped the red button. I went back and changed the auto limit to 130 and the manual to 165 and the dial on 5.5. I watched it for an hour and a half and it was still on, so I left. The cycles were definitely longer than before, but I didn't time them. I would have left it on six or set the auto limit a little higher, but with the temps hitting -12 tonight, I really just want it to keep running so that the trough will have heat. At those temps I expect icing on the ground.

The bypass valve hasn't been touched and is actually zip tied in a certain position between on and off, so I left that alone as I doubt it has ever moved.

I am sure that every situation is proabably a little different, but what is a good temp for it to be at? You mentioned the factory setting of 5 which is 143 degrees or so, but is that usually enough? I found that for me it couldn't keep up at 25 degrees outside when set at 5. When at 6, this morning it snowed 4 inches and all heated areas were clear.

I still need to top off the glycol, but am not sure what kind I need to use. Is there a certain kind that I have to put in, or do I have to know what's in there? I am really ignorant in that regards.

Thanks.

 

[I.B. Washincars]

What color is it? If it is green, it is most likely the same stuff you would put in your car (Ethylene Glycol). If it is pink, it is most likely RV type anti-freeze (Propylene Glycol).

 

[slash007]

It looks green, definitely not pink. I'll look around and see where I can find some.

 

[MEP001]

On some of those units, the relay that controls the pump has an off-delay meant to dissipate the heat from the burner into the system, and if that goes bad the unit will still run properly but it will trip the manual reset limiter after the burner shuts off. I've seen this happen quite a few times.

 

[2Biz]

Slash,
Do you have an Infra Red heat gun? Having one might help get everything set correctly. I know every system is different, but if this helps: I only have 95° glycol going out to the loops. By monitoring the incoming glycol that fires my boiler, it kicks on at 55° and turns off @ 70°. I have a 15° differential set on the Aquastat that controls this. This range keeps my floors ice free even in the coldest weather. The boiler stays on roughly 15 minutes and kicks off for about 15 minutes. The colder it gets, the off cycle is a little shorter and the on cycle stays on a little longer. It self regulates. This morning it was -10° and the weep running across the floor was not freezing. The boiler was off when I got there, so it still cycles on/off even at those temps.

Systems like you have is a lot different than mine, I know. I'm assuming it has a bypass valve to keep the temperature up in the boiler to keep from condensating like CB80 already points out. One thing I always keep in mind, if the Previous Owner knew what he was doing then he'd still probably own the CW! Given this, maybe the bypass valve isn't adjusted right! Using an infra red heat gun might help you get the temps needed to make your setup run the way it should. With CB80's recommendations taken into consideration, also. Finding the sweet spot takes a little time and tweaking....

 

[slash007]

Slash,
Do you have an Infra Red heat gun? Having one might help get everything set correctly. I know every system is different, but if this helps: I only have 95° glycol going out to the loops. By monitoring the incoming glycol that fires my boiler, it kicks on at 55° and turns off @ 70°. I have a 15° differential set on the Aquastat that controls this. This range keeps my floors ice free even in the coldest weather. The boiler stays on roughly 15 minutes and kicks off for about 15 minutes. The colder it gets, the off cycle is a little shorter and the on cycle stays on a little longer. It self regulates. This morning it was -10° and the weep running across the floor was not freezing. The boiler was off when I got there, so it still cycles on/off even at those temps.

Systems like you have is a lot different than mine, I know. I'm assuming it has a bypass valve to keep the temperature up in the boiler to keep from condensating like CB80 already points out. One thing I always keep in mind, if the Previous Owner knew what he was doing then he'd still probably own the CW! Given this, maybe the bypass valve isn't adjusted right! Using an infra red heat gun might help you get the temps needed to make your setup run the way it should. With CB80's recommendations taken into consideration, also. Finding the sweet spot takes a little time and tweaking....

Man, I'm jealous of your ice free floors I do have an infrared gun, but not sure what I am looking for exactly. Are you measuring the temp of the slap outside where the loops are? What temp are you looking for there? This morning it was still on, which was a good thing, but I did have 2 bays of the 5 freeze up and there was icing on the floor from the weep water. Brushes and tri-foam didn't freeze, but that is because the weep so much damn water. (I really need a blow out system) The boiler is set at an auto limit of 130 and the dial is at 5.5 which should be about 147 degrees or so. I do need to get it a little higher to prevent icing.

I also need to top off the glycol. It was suggested that I use concentrated anti-freeze and dilute it 1:1 with water. Would adding that to my existing glycol hurt anything?

My sight level on the glycol shows it to be about 1 inch below the red line. With my system, how much glycol should I need to add in order to get it back to the red line?