Low limit aquastat not calling for heat
Comments
-
Agree with @109A_5 about your photos not showing all the controls in the system.
@ericthor asked: "when the thermostat stops calling for heat and the circ pumps shut off, should it continue to heat until it hits the low limit setting of 160? mine is shutting down at 140, which is where the 20 degree differential is set at."
There are many ways to operate a boiler. We don't have enough information to answer this question and you have not provided any information about what control is operating the pump. The thermostat can not operate both a 24v. gas valve and a 120v. circulator pump by itself. There needs to be another control that your thermostat is connected to.
What is at the other end of the wire with the green arrow?
I don't think it is the thermostat. I think it is one of these:
PS. Nice rewire job on that photo @109A_5 (or should I say "you have learned well Grasshopper")
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
0 -
" when the thermostat stops calling for heat and the circ pumps shut off, should it continue to heat until it hits the low limit setting of 160? mine is shutting down at 140, which is where the 20 degree differential is set at. "
That may depend on what direction the water temperature was going, was it rising or falling. Also since the Low limit bulb is on a pipe and not in a well that may be an influence also.
If the temp was falling the Low limit may not call for heat until the water drops below 140. It may overshoot the 160 setting since the boiler may have to be hotter for the heat to migrate out the DHW pipe with no DHW water flow.
The thing is since the Low limit bulb is not in a well in the boiler and if there is no DHW water flow it may not quite work as expected or desired.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
@EdTheHeaterMan " PS. Nice rewire job on that photo @109A_5 "
Thank you.
" (or should I say "you have learned well Grasshopper"). "
There is some truth to that. I have noticed that folks often do better with a wiring pictorial type drawings.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System
1 -
i believe its wired into a Taco zone board. Ill send pics later today
0 -
" i believe its wired into a Taco zone board. Ill send pics later today "
That would make sense, the Taco zone valve controller would control the circulator for space heat only.
For best DHW / boiler performance, at some point, I try to put the bulb of the Low limit control back into the well even if the well needs replacing.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
that was the plan once heating season is over and I can drain the system down. Here’s a photo of the zone board
0 -
OK that makes sense.
It appears there is more than one load on the AUX PUMP 1 relay. If the loads are two circulators, I probably would have put one of them on another relay, to lessen the load on one relay, since it appears there are actually three relays active during a call for heat.
Either way there are spare usable outputs.
(Picture below)
The wire on the Left X - X goes to the boiler. The wire on the Right R and W goes to the thermostat.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
Another case of additional information added a piece at a time so we don't really get the full picture.
I see no reason to have a two zone control when you have only one thermostat. But there has been a lack of common sense from the beginning of this post. I can see one thermostat wire connected to Zone #1 and two line voltage wires connected to Zone 1 circulator output 120v. I followed the Red wire from Zone 1 circulator output to the 4" square box with a transformer added to one of the knockout openings on the bottom. There are no other wires entering that box, so I guess it is safe to say that when there is a call for heat from the thermostat the circulator operates, the 24 volt transformer gets power and the end switch closes to bring on the gas valve to ignite the burner. A less expensive relay, like the R845a or the Taco SR501 could do that, however this is what you have so we will go with it!
Now for the next big question. What does the 24 volt transformer power up? It appears to say “FANS 1ST FL” on the 4x4 cover. Does that operate a fan in an air handler? Is there ductwork involved?
And @109A_5 asked a great question earlier about the reason for maintaining a minimum boiler temperature of 160 °. Do you have a tankless coil for (DHW) domestic hot water inside that boiler?
Next clue will be the photo of the entire boiler far enough away from the boiler to see the pipes from floor to ceiling.
This may help @ericthor identify the wires inside the Taco Relay Box in order to answer the questions I just asked.
OR @ericthor may just be done with us now that the system is operating as he expects it to.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
0 -
I was thinking when there is a call for space heat from the thermostat the Taco SR502-5 energizes three 120 VAC loads via the AUX PUMP 1 relay. The Black wire under the screw becomes two black wires at the wire nut and also there is a Red Wire under the screw.
I suspect the three loads probably are;
1) A circulator. (one Black wire from the wire nut).
2) the 120 VAC to 24 VAC transformer on the box labeled “FANS 1ST FL” (Red wire).
3) A third unknown device, maybe another circulator (the other Black wire from the wire nut).
Probably have to chase out where the two left most BX cables go to understand more.
The boiler most likely has its own power so if either the Low limit or the Taco SR502-5 X - X is closed the boiler's burner fires.
I suspect @ericthor is happy since the system now basically works as it did before.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System1 -
Without the full undeeraatanding of how the controls in his system actually operate, I dont believe that @ericthor even knows what all those wires do or even how to determine where those wires go.
He may have a hydro coil, he may have a kickspace heater under the kitchen cabinet. Who knows what the "FANS" even are. Maybe he's the is a drummer in a rock band and every time his thermostat calls for heat there is a doorbell that rings and sounds like all of his groupies cheering for him at the last concert performance.
Regardless, his system is operating because of you @109A_5. You should be satisfies with that.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
0 -
My bad.. I have 2 fan driven units. each one has a rib relay. the second thermostat is controlling the the fans kick on.
0 -
0 -
Interesting. Besides the two Modines is there other radiation ? Lot of pipes (and large pipes) above the boiler. Two circulators, could be two independent zones, however depending on the space you are heating not sure if there would be any benefit. You also could have DHW priority, but if no showers (or other long DHW usage) it probably does not matter.
Not sure I'd put both circulators on one relay, I suppose if the specifications support it, its OK, just seem like unnecessary wear and tear.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
Awesome.
1 -
I'm not up on my gas codes, but that doesn't look safe to me. A locking gas cock on the line without the regulator might be a good idea. Why the two gas lines?
0 -
The photos answer some questions, However they pose even more questions.
How do two thermostats in the same location work? I can only see that one thermostat will get satisfied while the other thermostat never gets to heat the other zone or fan or whatever.
Both are set on 65° and one gets satisfied and the other also gets satisfied even though the other heating device is not operating. So as long as the other thermostat keeps the room where both thermostats are located at the set-point of both thermostats, the other heating device will never operate. This makes sense to someone somewhere, or those two thermostats would not be in the same place.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
1 -
Of course we can always speculate why there are two gas lines feeding that boiler. Are they coming from two different gas meters? Does the neighbor know you are using their gas meter from time to time?
additionally… why do you have two circulator pumps connected to one zone in that two zone control? The second zone circulator would work fine on that zone 2 circulator output. I'm sure there is a logical explanation to these questions
And to think about why this boiler needs to maintain a minimum temperature of 160° with a separate L4008A strapped to a pipe. This all makes sense to the gas company… that is how they make money. Selling gas. The more gas you use the more money they make.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
0 -
yes there there are a total of 9 radiators and 2 of the modine fan units. all other DHW is heated by seperate water heaters.
0 -
one of the 2 thermostats controls the temp at which the fans on the modine unit kicks on. we have it set to kick on a couole degrees below the main thermostat so that if and when the temp in the space drops (ie doors open) the fans kick on to help bring the temp up. mainly because they're so loud. id love to explore making them less noisy. perhaps a new motor.
the other gas source is running to a clothes dryer.
should the the 2 pumps be hooked to seperate zones? i dont really have a 2 zone system the way the piping and rads are laid out so it really doesn't make sense for me to zone anything.
The Grundfos pump was just installed to replace the leaky exact same Bell & Gosset you see on the other side.
0 -
it has been my understanding that the low level is to maintain i proper start up temp to avoid condensation.
0 -
That is one way to do that. It just costs a lot of money to keep a gas boiler up to 160° when there is no need for heat in the radiators. There are hundreds of thousands of what we call cold start boilers in the world. maybe even millions of cold start boilers in the world that do not maintain a temperature and they work just fine without condensation of flue gasses. Why is your boiler so special? and why do you need to spend thousands of dollars on gas, over the years, when there are less expensive ways to reduce the condensation of flue gas that don't waste gas energy.
As far as only having one zone is concerned. You do not need two circulators on that system unless there are two separate areas that have radiators in them. You have to know what areas are heated by each circulator. If you don't then all you need to do is to disconnect one of the circulators and see what radiators do not get hot.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
0 -
its survived with no condensation here in cold MN since 1994 with a low limit aquastat. i have no way of knowing that would be the case had it not been there. as far as the pumps are concerned, those have also been that way since before 1994. i dont plan on removing either.
0 -
Just because it's been like that for a long time doesn't make it right.
I'll put it bluntly. Everything you have going there is a complete mess of things not done correctly. It's inefficient and illogical. Ed is trying to explain to you how to correct these things so the system will be more reliable and efficient.
0 -
please be specific as to what is a complete mess and done incorrectly?
0 -
This may take some time but this is
Number 1:
The temperature/pressure gauge on your boiler is measuring the temperature of the water or air that is in the elbow above the boiler. When a standard boiler temperature/pressure gauge is inside the boiler itself. And how does the air in that elbow get out? i have a feeling that the temperature is that of an air pocket in that elbow.
Number 2:
The wire that is marked STAT os not from the thermostat. it is from the X X terminals on the Taco 2 zone relay.
Number 3:
The purple wire in the left photo has the insulation pulled back far enough that no insulation is under the screw, and the wire is positioned between the retaining washer and the screw.
The photo on the right has insulation under the screw terminal, and the wire is below the retaining washer. That shows that someone with poor electrical understanding and skills did this wiring.
Number 4: Incorrect use of Taco SR502 terminals
You have two pumps and a transformer wired to the AUX terminals at position A. The circulator should be wired to the Zone 1 PUMP terminals at position B. You could use the AUX for a boiler pump or a system pump that will operate whenever there is a call for heat from either zone. This is a clear misunderstanding of what this control is supposed to be used for.
Number 5:
Only using one thermostat and one zone in a two zone capable control when you clearly have two separate zones with two different circulator pumps
Number 6:
Really? You don't see anything wrong with this picture?
Number 7
Near boiler piping is obviously connected to an old gravity heating system. that near boiler piping should have had a bypass pipe with valves to adjust the return water temperature in order to get the return water temperature above 140° within the first 8 minutes of operation. This was not done at the time of the installation and never corrected during the 30 years it was in that location.
The repiping may have been expensive at the time it should have been done, but the lower-cost solution was to add an operating control to maintain a minimum boiler temperature of 160°. That only cost the price of the operating control at the time.
But no one talked about the cost of gas it takes to maintain that boiler temperature, which could add up to $300.00 per year extra. That is the equivalent of $9,000.00 over the thirty years it has been that way (and that needs to be adjusted for inflation over those 30 years).
Maybe that expensive repipe job 30 years ago may have only been $400.00 or less.
Shall I continue?
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
0 -
I appreciate everyones help. im going to leave the sytem alone as i feel at this point its really being critisized for problerms that arent really problerms.
i do not have a 2 zone system. The multi zone board was very inexpensive and is doing the job it was installed to do. also i explained why there a 2 thermostats next to each other more than once. the use of the low level aqua-stat cant be that foreign and out of line. why else would they make one and why would the boiler well have the option for one? also the wiring in the zone board is doing exactly what it is suppose to do, so i dont see the issue other than you'd prefer it your way.
there has been a lot of criticism and only one guy on here offered the solution regarding the original question/issue i had.
0 -
The problem has been solverd. thank you for all who offered help!
0
Categories
- All Categories
- 87.6K THE MAIN WALL
- 3.3K A-C, Heat Pumps & Refrigeration
- 59 Biomass
- 429 Carbon Monoxide Awareness
- 124 Chimneys & Flues
- 2.2K Domestic Hot Water
- 5.9K Gas Heating
- 119 Geothermal
- 168 Indoor-Air Quality
- 3.8K Oil Heating
- 78 Pipe Deterioration
- 1K Plumbing
- 6.6K Radiant Heating
- 394 Solar
- 16K Strictly Steam
- 3.5K Thermostats and Controls
- 56 Water Quality
- 51 Industry Classes
- 50 Job Opportunities
- 18 Recall Announcements