Honeywell Aquastar L8048G + (2) Taco Zone Valves - adding a 24V Common wire

KendallB

Trying to install a new Ecobee3 thermostat and have to run a "Common" wire up to the thermostat. Difficult to find any solid information on the Honeywell Aquastat L8048G online (just for the replacement controllers, which are not wired exactly the same as the L8048G).

Attached is a diagram of the current (pre-Ecobee3) wiring (boiler, Taco valves, thermostats) - want to make sure it is correct. I have seen some wiring diagrams that show alternate ways to wire the thermostats and Taco valves, so want to make sure my current wiring is actually correct. It always worked before, but want to make sure nothing is installed incorrectly/backwards.









The Aquastat has a built-in 24V transformer. How do I know which wire would be used for the COMMON wire? Assume blue wire on "T" would be the "Common"? If not, which wire/terminal would I use?

Assume I can pull a common from the Aquastat board/internal transformer, but not sure. If not, should I purchase a stand-alone 24V transformer or the FAST-STAT Common Maker?
http://www.fast-stat.net/

If that is the case, how would I wire one into the current system?

Please review the diagram and comment/correct as necessary. Thank you for any assistance you can provide.

Paul48

http://s3.supplyhouse.com/product_files/Taco-ZVC403-4- Install.pdf

GW

Yes this has been discussed in the recent past. The easiest thing get a zone controller like the Taco ZVC series. If you feel like your unable to pay for the "easy way" , then you can experiment with your existing Honeywell. If you smoke the control you'll probably wish you went with the Taco zone control.

Gary

KendallB

The boiler has seemingly been fine for 48 years using current controller and 2 zone valves. All I need to do is add a common wire, to run up to new Ecobee thermostat and looking for least expensive option. Can I tap into the current Honeywell board for the 24V common wire, or would the FAST-STAT Common Maker be a viable solution? I just can't find any technical docs on the Aquastat L2048G. The instructions on the back panel say to "see instruction sheet for zone control" - which I do not have a copy of. The wiring diagram also says "Max Load Tv to Z: 30VA at 24v AC

Paul48

What do you have for a zone control? We'll get you the instruction sheet.

GW

There isn't a 24v common terminal, that's the issue at hand. If you want to open up the control to grab onto the common, you're taking matters into your own hands. Just buy a control with its own new trans, keep it simple.

ChrisJ

You may be able to modify the controller, but I doubt anyone here will help you. To be honest, these controllers are very simple, if you can't track down where the common is, you shouldn't be doing it. I don't mean that as an insult, I just can't think of a nicer way to type it. It's not meant to be harsh.

The truth is, I doubt anyone here has taken the time to tear apart a controller either which I suspect, is what you were hoping for.


No one on here wants you losing your heat over a smart thermostat, especially this time of year.

If it was mine, I'd probably look at a way to grab a 24VAC transformer and use relays in the basement rather than modify anything. This would give the thermostat it's own power supply and the relays would control everything else, isolated.

KendallB

Hi Paul - the controller/relay is an Aquastat L8048G. The diagram on the back of the cover says to "for zone control see instruction sheet" (see photo) - which I am assuming means if you are planning to use the "Z" terminal on the Aquastat for more than one zone? I do not have any stand-alone zone controller - wired exactly as drawn above. Was hoping someone in the trade had original instructions for the L8048G to clarify how it is "supposed" to be wired.

Hi Gary - thanks for clarification on the common terminal. Was thinking I might have to tap into board to get the common, and didn't think that was wise, considering age of board, etc. Was hoping to keep costs (and effort) as low as possible. Just need 24V at thermostat, so figured stand-alone transformer or FAST-STAT Common Maker "might" be a viable solution. I understand new controller might be "best" way to go. . . but don't want to throw unnecessary $ at an inefficient 48-yr old boiler that probably should be replaced in the near future anyhow.

Other thoughts?

GW

I'm out of ideas, recently I was on a job trying to wire in a wireless thermostat. The module that communicates with the stat needed 24 v power. The boiler control was very similar to what you have. The TT was giving a true 24 volts, but that's useless. You can't use a TT leg for a common. The old controls didn't provide a c terminal. Well they did for the circulator and burner. If your burner is 24v you can give it a shot but most heating guys don't want to reinvent the wheel.

Anyway i just wired in a Taco, I'm not interested in opening up the control to see if I can grab a common.

Paul48

A Taco ZVC can be used with a new boiler. The Fast-Stat common maker can't be used, because you still need a common connection at the boiler. Even if you could use it, it would probably go in the garbage with a boiler replacement.

Tim McElwain

What is the voltage of the gas valve? Is it a powerpile gas valve?

The last time I did anything like this with an L8048G I ran a separate wire to the thermostat off the TV terminal (that is the "C" terminal on the built in transformer in the relay.). Test it first with a multimeter with no call for heat you should have 24 volts at that TV wire at the thermostat and the R wire (test it with it disconnected from the thermostat). Then with thermostat calling for heat see if you have 24 volts at #1 and #2 terminals on the Zone valves. Test this with those wires disconnected from the zone valve. Then try it with everything connected.