Vent damper opens but doesn't always close, normal? Slant Fin Gas Water Boiler

109A_5

Presently if I understand your system correctly the thermostat has no direct control over the boiler. The thermostat does control the circulator(s). So when a thermostat call for heat terminates the water flow stops, the pipes cool, the Tekmar sensor cools so the Tekmar thinks there is more demand on the system keeping the boiler going until the L4081B shuts the burner down on high temperature. This sounds like it will keep bouncing off the L4081B High Limit temperature setting all the time except when water is flowing (Tekmar temperature sensor control), this method does not seem correct and not very economical. And to make the economy even poorer the Damper was not closing.

Does this sound correct or am I missing something ?

I don't think you need any new or additional equipment, you just need what you have connected up and working correctly.

sixplex

Thanks for clarifying everything. That's exactly correct, you're not missing anything.

I just happened to have the exact length of BX wire lying around, I set it all up as per your diagram, everything seems to work as expected!

Does it matter how ZR/ZC is connected to L4081B?

It makes no sense to me that it would but the Sr504-2 manual says "Confirm polarity is consistent between boiler aquastat and switching relay.".

As i was testing, there was weirdness with the temp settings i currently have, Ecobee was calling for heat, but Tekmar wouldn't call to start the boiler, ironically because pumps weren't running to cool down the tekmar temp sensor below the Tekmar MIN because the boiler was too cool at the aquastat.

Should i set the Tekmar 256 MIN equal to DESIGN to fix the above? What should the aquastat min be set to?

My Tekmar 256 design temp is 150F (cast iron baseboard rads)

109A_5

" Does it matter how ZR/ZC is connected to L4081B? "

In this case Low Limit switch side of the L4081B is connected to the ZR/ZC terminals, either side of the switch could go to either ZR or ZC and the ZR/ZC terminal jumper is removed, and approved wiring methods used for 120 VAC is needed.

" It makes no sense to me that it would but the Sr504-2 manual says "Confirm polarity is consistent between boiler aquastat and switching relay. "

I believe that is when other Aquastat equipment is used. Your Aquastat is simply two switches. There are other more complicated Aquastats out there.

" As i was testing, there was weirdness with the temp settings i currently have, Ecobee was calling for heat, but Tekmar wouldn't call to start the boiler, ironically because pumps weren't running to cool down the tekmar temp sensor below the Tekmar MIN because the boiler was too cool at the aquastat. "

With the Ecobee calling the circulator(s) should have been running unless the boiler temperature was too low, in which case I would expect the Tekmar sensor to be cooler than the boiler.

Was the Warm Weather Shut Down active ?

I think I would set the Tekmar to what best describes your system. Better descriptions are in the manual.

I think I would set the Aquastat Low limit for 135 degrees Fahrenheit. That way it is below the Tekmar Boiler minimum. So the the boiler will at least warm up to 135 before the water is circulated. Once circulation stops with the end of a call for heat I would think the pipes would cool down faster than the boiler, as you noted in a previous picture.

You may have to do some experimentation to see what serves your needs best. You don't want the boiler water too cool.

At least now you won't be using fuel just to keep the boiler at 175 Degrees when there is no call for heat.

sixplex

"Was the Warm Weather Shut Down active ?"

Not sure. Will have to keep an eye on it.

Thanks a lot for all the help once again. Very happy with the changes and learning so much about the boiler.

I will report back here once i have some measurable stats to share, should be useful for anyone wondering how much of a difference these changes make.

109A_5

Hopefully you will see a noticeable reduction if fuel use, especially during the shoulder seasons. Maybe even more even heating.

sixplex

25_03_2025_66 Slant Fin Wiring Diagram Supplied at Installation.pdf

Found the original boiler paperwork, according to the included wiring diagram the boiler was installed correctly.

Specifically, the aquastat is supposed to kill power to the transformer/ignition/damper on high limit.

Also all the safety switches are on the blue wire going from TT to damper and not on the red wire going to the ignition model.

Boiler was installed in 2007.

What gives?

109A_5

OK, that looks like an older drawing.

One - production changes do happen. The drawings we were working from look newer.

Two - the installation of the Tekmar messed up the original control logic by moving the thermostat away from the burner circuit and to the circulator(s) only circuit, leaving the boiler with no demand control. The Tekmar 'Demand' was just jumpered.

The intent of that wiring method (the older one just posted) was to keep the boiler's water temp between the Low and High limits. If the Boiler's water was below the Low limit the circulator(s) would shut off. As it does now too. The Low limit switch was not even connected in your pictures.

If the boiler's water temperature goes above the High limit the boiler would shut down. When the High limit re-closed (the circulator(s) stays running with the High limit open, cooling the boiler), and if the thermostat was satisfied the Damper would then close.

With this older method the circulator(s) runs the whole time until the boiler's water temperature is below the Low limit. Cooling the boiler this way may cause a greater overshoot in the heated space depending on the Thermostat's Heat Anticipator settings.

Since the way it was with the absence of the thermostat in the boiler's control the boiler kept running until the High limit shut it down, only to keep it cycling this way when the thermostat did not command the calculator(s) on.

I would expect the way it is presently you would get better economy and better comfort. I will think about it some more.

109A_5

In the context of the thread title;

" Vent damper opens but doesn't always close, normal? Slant Fin Gas Water Boiler "

If the boiler, thermostat and the circulator(s) were wired as the older wiring diagram shows, then when the thermostat is satisfied and the High limit is not tripped the Damper would close, since the transformer would remain energized. If during a call for heat the High Limit trips and shuts off the transformer the Damper would not close, but the High Limit Tripping would not be a persistent cyclic event like it once was. So as soon as the thermostat is satisfied and the High Limit resets the Damper would close.

The way it ended up (until recently) with only the Tekmar controlling the boiler and the thermostat only controlling the circulator(s) it became a bit dysfunctional IMO.

sixplex

Makes sense.

I figured figured out why i was having an issue with this setup initially. The Tekmar sensor was strapped to the pipe and covered with insulation, that reading wasn't accurate enough for it to work well. I put the sensor in a thermal well that was already there, the sensor fits in there very loosely which i'm not sure is ideal but everything seems to work well now.

When it's 33F outside, when the boiler starts the 140F supply returns at 90F, the aquastat now shuts off the pumps multiple times before the return temp gets warm enough.

Is that a good enough way of protecting it or would i benefit from something like a thermal mixing valve or a delta t circulator ?

Efficiency aside i don't know how the boiler is still alive after 18 years without any protection before this change.

109A_5

" Is that a good enough way of protecting it or would i benefit from something like a thermal mixing valve or a delta t circulator ? "

Is this the same place with the Monoflo piping ? If the flow is reduced too much the Monoflo may not work correctly.

You may have to raise above the recommended temperatures and the Low Limit to help protect the boiler.

" Efficiency aside i don't know how the boiler is still alive after 18 years without any protection before this change. "

I think that it was maybe too hot most of the time, at least during the time the Tekmar was installed, cycling the High Limit a lot. Probably good for the boiler but bad on your fuel bill. You may have to find a happy middle place, at least now it is more adjustable.

sixplex

"Is this the same place with the Monoflo piping ? If the flow is reduced too much the Monoflo may not work correctly."

yes, you're right that's always a concern. i have a split return on the monoflo, with completely blown gate valves on each one, originally mean for slight balancing and isolation to do air purging, i'd love to replace them with balancing valves to slightly fine tune each return but full port ball valves are a much safer bet because they wont restrict the flow

"I think that it was maybe too hot most of the time, at least during the time the Tekmar was installed, cycling the High Limit a lot. Probably good for the boiler but bad on your fuel bill. You may have to find a happy middle place, at least now it is more adjustable."

possibly, but also the original installer set the high limit to 170, from what i've seen 180 is the more common, that may be also why the high limit was reached so often.

109A_5

There is some interesting dynamics going on with your system, Tekmar control (minimizing water temperature when desired), Monoflo characteristics, maintaining above a minimum boiler temperature and return temperature as much as posible.

You want the boiler temperature out of condensation range and the return water temperature not too low also. You want enough water flow so the monoflo works correctly. The wiring diagram that came with the unit seemed to just control the circulator to maintain boiler temperature above a minimum level. As it does now.

There may be more eloquent ways to do it now, and even that has options. I would certainly do some research.

A thermal mixing valve may be hard to implement with a monoflo system, due to flow restriction and/or redirection from (bypassing) the monoflo radiation.

109A_5

" possibly, but also the original installer set the high limit to 170, from what i've seen 180 is the more common, that may be also why the high limit was reached so often. "

It seemed to me that when the circulator was running the Tekmar would manage the boiler to control the water temperature, and I would expect it to be under 170 degrees (depending on the outdoor reset) with Tekmar control. When the call stopped the water stagnated and cooled near the Tekmar's sensor probably keeping the boiler running much longer than needed, only to be stopped by the 170 degree High Limit. To me keeping the boiler at 170 degrees when it should be idle is not very economical, at least fuel wise.

Hopefully you would only need 180 degrees on the coldest days. With it set to 170 degrees, on the coldest days did the system have any problems heating the structure ?

sixplex

That sounds about right, we'll soon find out how our changes affected the fuel usage. The changes were made roughly when i got my last gas bill, when the next one comes in i'll compare it to last year taking the temperature into consideration.

"With it set to 170 degrees, on the coldest days did the system have any problems heating the structure ?"

Never an issue. I thought it was oversized and used the slant fin app to confirm heat loss, the boiler size is apparently right for the building.

The following is how much the 2 ecobees zones were calling for heat during a cold week in Junuary, -10C.

109A_5

This call seems long, maybe 6 hours continuous, why the difference with the rest of the day and the other thermostat ?

I think the design day temperature for the GTA is about -17.5 C.

sixplex

Good catch.

That's actually the smaller zone which is set 1C lower a night, Ecobee starts working on it in advance to bring it back up to temp which takes longer than maintaining temp, allowable drop is set to 0.3C on ecobee, which is the most the other zone has to make up.

Being the smaller zone i think the boiler spends a lot of time hitting the high limit when working on that zone, the entire call takes longer.

Another factor, the flow is likely wrong through that zone. First 6 rads are almost all the way closed in an effort to "balance", they were massively overheating the space before, the last 4 rads are wide open. That zone is also below the main (2 monoflo tees per rads = more head) and there is a fair bit of magnetite(black sludge) sitting at the bottom of those rads. The pump is taco 0015e3 set to medium (007 equivalent). That's why i was thinking of getting the Taco delta t pump (VT2218) for both zones, conflicted if that actually makes anything better at the expense of increased complexity and more points of failure (temp sensors).

Upper image - Smaller Zone (1 Floor) - Downstairs - 22C during the day, 21C at night

Lower image - Bigger Zone (2 floors) - Upstairs - 22C all day

-17.5 or -20 is about right for design temp in Toronto, although it's been getting warmer and warmer.