Troubleshooting A-stat, Honeywell L8148A

Reply

  #1  
Old 12-05-12, 06:10 PM
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 6
Received 0 Votes on 0 Posts
Troubleshooting A-stat, Honeywell L8148A

I'm not overly familiar with boiler systems. This is an old oil fired boiler. I took my volt meter to the aqua stat and saw that I had 120 volts coming in. No voltage getting to the circulator or the burner. I noticed a "manual" lever/button on a relay and pushed it in and both burner and circulator started running. So, I guess this relay isn't getting power to fire it up. What feeds the power to this relay? The t-stat wires read in the a-stat read 30V on the AC setting of the voltmeter. (or should I be reading that in DC?)
Any information would be greatly appreciated.
SteveH
 
Sponsored Links
  #2  
Old 12-05-12, 06:21 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
Hi Steve, AC is correct. The power for the relay comes from the small internal transformer.

How is your a'stat controlled? In other words, what is wired to the " T T " terminals? A thermostat? Wires from your zone valves?

If it's a single t'stat, have you changed the batteries yet?
 
  #3  
Old 12-05-12, 06:35 PM
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 6
Received 0 Votes on 0 Posts
Thanks.
It's an old t-stat too, mercury switch, so no batteries (that i saw).
It looks like the t-stat wires go to a small transformer (?) on the side of the boiler, into the a-stat. There are two zone valves, and I remember seeing the t-stat wires tied into both z-valves. I'll be back over there tomorrow. I did have the 30 volts on the t-sat connectors inside the a-stat.
Thanks . . . I just hate to replace the a-stat and have it be something else (I'm a mechanic and like to verify before I buy)
 
  #4  
Old 12-05-12, 07:10 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
OK, I don't think you have a bad aquastat.

I don't think I need to say this, but:

WARNING! 120VAC EXPOSED VOLTAGE INSIDE AQUASTAT AND ELSEWHERE ON BOILER CONTROLS! DO NOT TOUCH ANY EXPOSED TERMINALS! YOU CAN BE KILLED! IF YOU HAVE ANY DOUBT ABOUT YOUR ABILITY TO NOT KILL YOURSELF, STOP HERE AND CALL A TECHNICIAN!

Here's what you have (IF you have Honeywell (and some other manf) zone valves)

If you have some different zone valves, tell me what they are...



With a multimeter, measure the output of the transformer on the side of the boiler. You should have nominal 24VAC there. If not, verify that there is 120VAC at the primary side of the transformer.

If you have 120VAC on the primary, but you do not have 24VAC at the secondary of the transformer, the transformer needs replaced. Do not use a doorbell transformer. You need a 40VA control transformer.

If the transformer checks OK;

Take a short piece of wire, and VERY CAREFULLY jumper the T T terminals in the aquastat. Be prepared to hear the aquastat relay click in and the boiler to fire up. If so, your aquastat is fine.

Do these and let me know...
There will be more.
 
  #5  
Old 12-06-12, 02:59 PM
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 6
Received 0 Votes on 0 Posts
OKay, back at it. The transformer is fine, 120vac input 24vac output.
The jumper wire across the t-stat fired everything up. So I guess the a-stat is good.
 
  #6  
Old 12-06-12, 03:12 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
Yes, I believe it is...

So now, remove the valve cover and adjust the valve lash... oh wait... wrong forum! never mind me...

If you have some different zone valves, tell me what they are...
What is the make/model of your valves?
 
  #7  
Old 12-06-12, 03:17 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
How it works

Zone valves have a motor and an 'endswitch'. The endswitch CLOSES when the valve OPENS.

When a thermostat calls for heat, it completes the circuit from the transformer to the zone valve motor. (it's just a switch)

When the valve opens, the endswitch which is wired to the boiler control CLOSES, basically doing what you did with the jumper.

You have tried BOTH thermosats, and NEITHER of them fires the boiler?

If NEITHER is working and this occured suddenly, I'm thinking you have a bad wire connection.

Your system is probably wired up in what I call the "rat's nest" method. There are probably a bunch of wire nuts. The wiring is all probably solid 18ga thermostat wire. What often happens is one of the wires will break right inside the wire nut. You won't see it because the wires are twisted and the broken one won't be hanging loose.

First inspect the wiring by removing one wire nut at a time (TURN POWER TO BOILER OFF FIRST!) and carefully inspecting for broken wire. Since BOTH are not working, if there is a broken wire it will be one on the COMMON wiring to both valves.
 
  #8  
Old 12-06-12, 03:38 PM
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 6
Received 0 Votes on 0 Posts
Okay. I'll head back over. I'll check the upstairs thermostat also. When I turn the power switch on to the boiler, I do hear one of the zone valves activate. YES, to the rats nest. I'm not impressed with the mess and will clean this up as I re-do all the connections. Heading back over now and see what I can come up with. Thanks so much!
 
  #9  
Old 12-06-12, 03:40 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
I guess no internet over there and no 'smart phone' ?

If you hear the zone valve activate and the boiler doesn't fire, it means a defective endswitch in that particular zone valve. ESPECIALLY if the other zone valve works properly.

OK, keep us posted.

But, you still haven't answered my question of make/model of zone valves?

IF you have Honeywell zone valves the YELLOW wires are the MOTOR and the RED wires are the ENDSWITCHes.

Unless you have the "F" models of the Honeywell, in which case there will be a labeled terminal strip on the valve cover.
 
  #10  
Old 12-06-12, 04:46 PM
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 6
Received 0 Votes on 0 Posts
Okay, we bought the house across the road from us for family/rental/whatever, wanted to have some control since that house would be our only neighbors. No phone there, no internet there, and my smart phone isn't so great out here in the middle of nowhere : ) terrible reception and our wireless router doesn't make it that far . . .
Okay back to the problem . . .
I missed the post asking about the model of the valves, but I was coming over here to ask about that. There's got to be a way to bypass/jump/check each zone valve and end switch . . . right? Yes, they do have 2 red wires and a yellow and an orange wire. The "first" zone valve in line has what looks to be a "junction box" on the end of it. Everywhere I check, I get 24 volts. I did find one bad wire connection, but that wasn't it,. When I check T-stat wiring, I check pos VM wire on red and neg VM on white right? check as a set? Sorry, I know this probably isn't that hard, but I'm trying to wrap my head around what the end switches do to break the loop. Obviously they break one of the T-stat wires. I took my jumper wire and tried to jump between the different connections to see If I could eliminate a bad valve/end switch, but didn't do it right or didn't quite understand the end switches.
 
  #11  
Old 12-06-12, 05:16 PM
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 6
Received 0 Votes on 0 Posts
OKay . . . Found it! Re-read all your replies (Thanks so much!) and went back over and wrapped my head around it. The second zone valve had a red wire that was not connected to a T-stat wire, no wire nut on the floor no nothing, and the wires were way far away from each other. Amongst the rat nest and not understanding the valve wiring, I thought this was how it "always was." Not sure how it came apart (bungie jumping mice?) but you were right. Sorry for the wild goose chase . . . and thanks so much again, you are wonderful.
Steve
 
  #12  
Old 12-06-12, 05:54 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
Thanks for the kudos Steve, but you done the work! I just tolt ya what to look for!

Glad it was an easy fix!

Just perhaps a bit more explanation:

On a system with zone valves such as yours, there is no ELECTRICAL connection from the thermostat to the boiler.

The endswitch is completely isolated (at least on Honeywell 'type' valves it is, there are exceptions) from the thermosat/motor/transformer.

Motor turns, CAM (hey! that's a mechanic word!) pushes the endswitch, endswitch fires boiler.
 

Last edited by NJT; 12-06-12 at 06:30 PM.
Reply

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:
Description:
Your question will be posted in: