Connecting a Taco Switching relay to a honeywell 8148A aquastat.


Old 08-26-13, 06:03 AM
Thread Starter
Join Date: Oct 2011
Location: USA
Posts: 62
Received 0 Votes on 0 Posts
Connecting a Taco Switching relay to a honeywell 8148A aquastat.

I've recently rebuilt my heating system with the addition of a wood boiler and new supply/return headers. I've simplified the wiring by adding a Taco SR506-4, six zone switching relay.

I left all the boiler controls alone, including the honeywell 8148A aquastat. Out of the aquastat was 20 gauge T-stat 2-wire and 12 gauge for power. Without looking at the internals of the aquastat, I assumed the t-stat wire was used to start the boiler and the t-stats themselves were powered from a small transformer mounted on a 4 square plate at the power source (since removed with 24v now supplied by the switching relay). I followed the wiring diagram for a cold start boiler, using a jumper on ZC/ZR and connected the T-stat wire from the 8148 to the end switch on the switching relay ( to "TT" on boiler).

I powered the switching relay and jumped the t-stat terminals to check if each circulator was working appropriately & to check zone 6 "priority" was functioning. I then turned the oil boiler on, which powered the 8148 aquastat, jumped a t-stat to check operation and heard a loud buzzing coming from the aquastat. I popped the cover and noticed the aquastat had a transformer and 24v is emitted from the 2-wire when power is applied.

So, I have 24v coming from the end switch on the switching relay (whenever a zone calls for heat), and 24v coming from the aquastat when the oil boiler is powered. Anyone know how to re-wire?
Sponsored Links
Old 08-26-13, 03:09 PM
NJT's Avatar
NJT is offline
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
Something isn't adding up.

I have 24v coming from the end switch on the switching relay (whenever a zone calls for heat)
That should not be.

Note that the Taco panel says "Isolated End Switch" (the X X terminals) and what that means is that there is no, or should be no voltage coming OUT of the Taco on those two terminals. The X X End Switch is simply a 'dry' set of relay contacts.

Remove the wires from the X X on the Taco and power the Taco and measure the X X. You should see NO VOLTAGE coming out. If you do, something is wrong with that panel. If no voltage coming out, go to next step, otherwise stop here and try to figure out why you have voltage coming out of the Taco.

If you switch your meter to OHMS you should see OPEN when there is no zone calling for heat, and ZERO ohms when any zone is calling for heat.

What happens when you jumper the T T terminals on the 8148 together? Still get a buzz?

SOME buzzing is normal. Transformers buzz, relays can buzz... it shouldn't be LOUD though.
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: