Wiring relay to cut heat call during DHW (combi boiler)
Hi All,
Thanks for the continued help on this site.. decades of great info!
So I have a Navien NCB 240/130H which replaced a CH240. Previously I had it wired up to a time delay DPDT relay so to cut the W wires to two air handlers (upstairs and downstairs) to kill heat calls while we took showers etc in winter. The CH240 was wired per the diagram below (I honestly can't remember why it was so complicated w/ jumpers etc… other than I tried multiple combinations to get it to work and I was more of a **** back then than now :D)
The new NCB has 2 A/H contacts which close during a heat call, and open when there is a DHW call OR the boiler is not supplying heat. I believe this is normally to open G to cut fan during lack of heat. Using the same relay, is it as simple as wiring a 24v red to "A", and "T" and "B" connect to the A/H contacts? (opening and closing the ground to energize the relay)
Thanks for any advice!
OLD WAY (CH240 circa 2012) - disregard the colored dots on the "T" and "RD" contacts on the boiler, bad edits from an older failed version
Comments
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Should not need it.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
The problem is not the boiler… I need a way to cut the heat call so that the air handler does not blow cold air.
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OK, may not need the timer. Since you are switching two independent circuits you probably still need the relay.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System
1 -
Maybe this.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
Actually you probably want the timed delay, so on a call for heat the air handler does not blow cold air until the heat exchanger heats up, so probably hook it up the same way as it originally was.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System1 -
I think controlling the air handler fan via a strap-on aquastat on the air handler return pipe will solve this problem, as well as anything similar.
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Have tried this and it's not always reliable… the relay worked well in the past so prefer that route
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What is the model number of the air handler? Sometimes I can add a Button Type Limit reverse limit to the return pipe so, along with a heat relay in the air handler, bring on the zone pump (or valve) and fan on a call for heat from the air handler. Then, when the DHW demand happens on the Nevian, the CH circulator pump stops and the water gets cold and the reverse limit stops the fan, until the pumps start to send hot water back to the duct coils.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Yes the timer has worked well. I should have added it's for two air handlers set up for hydro heat (if not already clear).
And sorry was not clear, that's the OLD setup (the CH240). The NCB has this setup. BTW if I recall the connecting to just A and B did energize the relay but didn't switch anything… the T needed to be connected in the circuit. The CURRENT model has these terminals below, so trying to figure out what will work
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handlers are both Trane TAM7s (actually the American Std version but same same)
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Problem is the terminals are different as its a newer model. I think there is a TS heat somewhere else on the board so I can go back to that if needed, was just looking for a less jury-rigged way
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The TAM 7 has the ability to use a Communicating thermostat or a Legacy thermostat. what thermostat do you have?
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
0 -
Also you can have an American Standard OEM coil or a after-marker add on coil. Are you using the Am Std Hydronic coil?
This coil has the temperature sensor already included (as an accessory that the installer must connect) and the TAM7 circuit board has the programing to accomplish what you want to do without adding a bunch of relays and temperature sensors.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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It's a factory slide-in coil which comes with a hydronic control board. I do have the temp sensor but it is not very effective (and no way to adjust the temp).
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the temp sensor is not adjustable. it is there just to let the controls know that there is hot water in the coil so the fan does not blow cold air. I believe it is set for about 100°F
Let me look at the Navien wiring and the TAM7 wiring to see the best matchup.
Also, what is the thermostat you have? Does it have two or three stages of heat? W, W2, W3. That may be a factor to deal with if you do. The different stages turn up the fan to a higher speed to deliver more heat to the rooms.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
1 -
Sorry forgot the stat… they are Ecobee 3s, only W1/W2. The staging on the board is already jumpered for an EXTERNAL coil (as if I had a top mount coil like in your instruction link… but I don't, I have a slide in). Net effect is max fan. I've always wanted to tune that as well, but have not got around to it, and with long runs/old house it works fairly well.
And yes the temp sensor clip is purely an all or nothing proposition. But I can say for sure I've wired it correctly and it's never made a difference - never turned off anything even when it was ice cold. Never figured out why other than the mix of the hydro board and handler boards are a little finicky… hence my hope to get the relay working again as it did under the old boiler
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Not sure I understand the problem here it appears both boilers have 24 VAC access and A/H relay contacts, apparently they are just in a different place in the new unit. It looks like the timer needs a constant 24VAC and the A/H relay contact closure (switched 24 VAC) activates the trigger input (on the timer) to start the delay function of the timer.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
There is a lot to digest on the Navien Air handler interface. And it dies not account for central air conditioning, which I assume you have. I am inclined to set this up so the air handler gets the most out of its capabilities and just turn on the pump for the CH zones with an end switch from the TAM7 heat relay or Hydro coil relay.
The temperature sensor on the slide in coil is one of two ways that the fan will be allowed to operate. there is also a time delay that can run the fan on the TAM7. So if the TAM7 calls for heat and the hot water takes longer than the time delay, then you may get some cold air from the duct work. I'm researching that for you to see if you can set a longer time delay to reduce the blowing cold air issue.
Ecobee thermostat is Legacy wiring. that makes it easy. thanks
This will take a while. Look for my diagram tomorrow morning
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
0 -
How many pumps do you have? A pump for each air handler (total 2) or one pump for both air handlers with two zone valves?
Do you know if you are using primary secondary piping so the boiler has a pump and the air handlers have a separate pump(s)
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
0 -
I assumed that each air handler has a zone pump. If there is only one pump and you have zone valves, I can change the diagram to reflect that configuration. Based on the information in both manuals and the slide in coil manual, This is what I have come up with. I did not read how to configure the Dip Switches but it seems strait forward to get where you need to be
I want you to see if connecting the W2 on the Ecobee to the W2 and W3 on the air handler will work (Brown Wire). But there may be a problem with that when there is a call for DHW priority. If the fan blows cold air during a DHW priority, then place the jumper back between W1 and W2 in the TAM7 and disconnect the Brown wire (See Note 2)
If you have any questions I will be online after 10:30 AM Eastern USA
Hope this is easy to follow.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
1 -
Yes turns out that's correct. I ended up doing this which seems to work. The ONLY problem (which I now remember being a problem with the old boiler) is that the boiler will not ramp up heating water if the outdoor reset is enabled. It also clicks the relay on and off every several minutes for reasons unknown. Not sure why or how this is other than perhaps ODR requires a different configuration.
I can probably do the same thing in reverse (using the normally open relay terminals to cut W) using the DHW PRI block below the A/H, as those close only when the boiler is heating DHW.
Still not sure why I didn't do exactly the same thing on the original boiler, or why it wouldn't work the same, but I can barely remember last week much less 12 years ago :D
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Thank you this is really above and beyond! There are two pumps total (one for each handler) but complicating things a big is that the downstairs is split into two zones, so there is also a zone controller involved. I am always looking to improve the hack job that my original installers did so I do want to dive into this diagram.. I have long been interested in getting staging to work because I think setting the fan to max (jumpering W1-W3 and setting for external coil) was a lazy choice by said hacks, and that greater efficiency could be gained.
Cooling works pretty well as is… unlike heat there is a 30 sec fan run to purge the cold air and I assume to allow the evap coil to not freeze up. Both handlers shut the heat off pretty much instantly or it seems so… it used to run for several minutes to purge heat because the hacks used the wrong type zone controller (for a heat pump setup w/ backup heat), but I replaced it w/ a proper one. I THINK I can set it to purge if I really need but so far it has not been a problem on either handlers.
Thanks again!
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" It also clicks the relay on and off every several minutes for reasons unknown. "
If it was cause by the old boiler, it may have been a software issue, the new boiler may not have that issue. It could be the timer too, but I hope not. If it still does it you could easily verify the source with a multi-meter.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
This is only when outdoor reset is enabled (on the new boiler AND the old). For some weird reason it doesn't like anything connected to A/H while ODR is on.
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My impression from the manual is the A/H is just a relay and the terminals you connect to just go to the relay contacts. So I would imagine the odd A/H behavior would be there even if nothing is connected to the A/H terminals.
Maybe a different outdoor reset curve would help if available.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System1 -
downstairs is split into 2zones.
Are you referring to two ductwork zones using dampers? If yes, what is the model number of the control that the thermostats connect to and the zone dampers connect to?
That will determine how to set the dip switches on the TAM7
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
0 -
Correct… two duct zones. The ZC is a Honeywell HZ432K which controls everything downstairs
1 -
You have 3 thermostats are all three Ecobee?
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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One is actually an Amazon, but same idea… it also has only W1/W2
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Then I have this Diagram that should do the job to gat your new boiler to do what you want it to do.
Click on the Photo and you should be able to zoom in for the details. The same issue about the W2 on the air handler (brown wire) may cause the fan to blow cold air on the DHW Priority when the circulator pump(s) shuts down. If that happens then disconnect the W2 from the thermostat and just put the jumper from W1 to W2 on the TAM7.
There may be another thing that will make the system more efficient at the fan speed selection by using only W1 from the thermostat, then adding a time delay to jump to W2 and a second time delay top jump to W3. If you are interested in that I could suggest the proper parts. Let me know.
If you are not connected this way, you may want to change your setup to this design. Especially the circulator pumps being connected to the Navien and not the Honeywell Zone Control. It should be able to use all the features of the Navien and the TAM7's important features in order to make your home more efficient and more comfortable.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
1 -
Thanks so much Ed! I spent tonight mapping out all the existing wiring so will dig in soon!
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A differnt ODR curve was the answer. Forgot I had it set to high mass radiant (during experimentation to get it to a point where Return water was condensing) which is the lowest overall setting. Giving it a go with Cast Iron Baseboard
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