Troubleshooting Honeywell L8148A aquastat


  #1  
Old 01-21-15, 08:37 PM
T
Member
Thread Starter
Join Date: Apr 2011
Location: USA
Posts: 67
Likes: 0
Received 0 Likes on 0 Posts
Troubleshooting Honeywell L8148A aquastat

The thermostat is set to 65 and the house temp reads 62. Some of the radiators are tepid, others are cold.


The oil burner comes on, and if I hold my ear close to the TACO pump, I can hear it faintly whirring. The pressure starts to build. The outgoing pipe gets too hot to touch. The return pipe also gets pretty warm, but doesn't burn my hand. When the pressure reaches 180, the oil burner cuts off, and the pressure continues to build to 220. Slowly, over the course of 20-30 minutes, pressure drops down to 120.

When I check the (brand new replacement) zone valve with a multimeter after the burner cuts off, red+white reads 28.5V and red+green reads 28.5V. If I understand correctly, that means the zone valve is calling for circulation. Is that right?

But it seems that the circulator is cutting off as soon as the burner goes off, even though the zone valves are calling for circulation. At least I don't hear the faint whirring. Shouldn't the pump continue to circulate the hot water after the burner cuts off?
 
  #2  
Old 01-21-15, 08:45 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 14,403
Received 39 Likes on 37 Posts
Those are temperature numbers, not pressure. That gauge should have another set of numbers. Here is how to check the pressure or verify the accuracy of the gauge. http://www.doityourself.com/forum/bo...ure-gauge.html
 
  #3  
Old 01-22-15, 05:56 AM
T
Member
Thread Starter
Join Date: Apr 2011
Location: USA
Posts: 67
Likes: 0
Received 0 Likes on 0 Posts
Sorry, I should have said the pressure rises to where the temp reaches 180 and then 220.

After further investigation, the electrical readings look OK (T-T, C1-C2, and 2-3 on the zone valve) it looks as though the mechanical contact switch in the Honeywell L8148A Aquastat is acting flaky. It has vibrated and buzzed since the first day the heating company installed it about 8 years ago, and they told me not to worry about it. Last night, I tapped it down during a call for heat, and the circulator pump came on.
 
  #4  
Old 01-22-15, 07:51 AM
T
Member
Thread Starter
Join Date: Apr 2011
Location: USA
Posts: 67
Likes: 0
Received 0 Likes on 0 Posts
Troubleshooting Honeywell L8148A Aquastat with multimeter

I am trying to find out what our L8148A should be doing and whether it is doing it.

House is cold. 61 degrees. Thermostat is set to 66.

When the boiler is firing (pressure rising from 120F to 180F) the reading on the TACO zone valve 2-3 terminals changes to ~ 25V, and I can hear a faint whirring in the TACO circulator, if I hold a short length of copper pipe against my ear and place it against the pump, like a stethoscope.

The radiators get warm. The return pipe gets hot.

But when the boiler reaches 180F, it cuts off (per the Aquastat's setting) and then the circulator also cuts off. Shouldn't it keep running when the house is 5 degrees below the thermostat setting?

When the boiler has cut off, and the temperature has started to drop (it's around 150F), I take some multimeter readings:

The T-T reading is 0.001V. Isn't that a "call for heat"?

The C1-C2 reading is close to zero: 0.02V. Does that mean circulator is not getting any juice? Not being told to circulate?

The 2+3 reading on the TACO zone valve is also close to zero 0.01V. Does that mean the zone valve is being told to stay shut?
 
  #5  
Old 01-22-15, 08:55 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,538
Likes: 0
Received 8 Likes on 6 Posts
The new thread you started contains a lot of the same information as your previous one. There's no need to start a new thread with every question. I've merged the two threads, please continue with the same issue in the same thread.

(pressure rising from 120F to 180F)
You keep calling temperature pressure. Pressure is PSI and temperature is DEGREES.

Taco zone valves:

When there is NO call for heat from the thermostat you should see appx ZERO VAC between terminals 1 and 2

When there IS a call for heat you should see appx 24VAC between terminals 1 and 2

Remember that ALL zone valves terminals 2 and 3 are connected in PARALLEL, so...

When ANY zone valve is OPEN (calling for heat) you will read ZERO volts on terminals 2 and 3

When NONE of the valves are calling for heat (ALL CLOSED) you will read appx 24VAC on terminals 2 and 3

ALL of the zone valve terminals 2 and 3 in parallel are connected to the T T terminals of the 8148 so you should see the exact same conditions there at the T T as you see on terminals 2 and 3 of the zone valves.

But when the boiler reaches 180F, it cuts off (per the Aquastat's setting) and then the circulator also cuts off. Shouldn't it keep running when the house is 5 degrees below the thermostat setting?
Yes, if everything is correctly wired, when the BURNER cuts off at high limit, AND there is a continued heat call the circulator should run until the thermostat is satisfied.

The T-T reading is 0.001V. Isn't that a "call for heat"?
Yes, it is.

The C1-C2 reading is close to zero: 0.02V. Does that mean circulator is not getting any juice? Not being told to circulate?
That is correct. If the circulator were being told to run you would see appx 120 VAC at the C1 and C2 terminals.

The 2+3 reading on the TACO zone valve is also close to zero 0.01V. Does that mean the zone valve is being told to stay shut?
Terminals 2 and 3 are not 'telling' the zone valve anything. Terminals 2 and 3 are doing the talking. They 'tell' the boiler to fire or not.

Terminals 1 and 2 on the zone valves are the 'listeners'. The THERMOSTAT is what 'tells' the zone valve to open when it sends 24VAC to them.

When the zone valves OPEN after being told to, they flip an internal switch that is wired to 2 and 3. This internal switch is what 'tells' the boiler to fire.

Terminals 2 and 3 reading ZERO volts is telling you that ANY ONE of the zone valves is OPEN. Remember that all the zone valves 2 and 3 are in parallel so what you read on one, you will read on ALL.

If you see zero volts on 2 and 3, it means AT LEAST ONE (and it could be MORE than one) of the zone valves is OPEN and calling the boiler to provide heat.
 
  #6  
Old 01-22-15, 09:19 AM
T
Member
Thread Starter
Join Date: Apr 2011
Location: USA
Posts: 67
Likes: 0
Received 0 Likes on 0 Posts
Thanks for the multimeter/value/aquastat info.

Sorry about temp/pressure mixup. I know the difference (and the relationship) but am frazzled at the moment, because the readings and behavior have been so erratic.

But I have found the problem!

There is apparently a short in the circuit board. When I press up gently with a small piece of wood against the magnetic relay (not the switch at the top, which clicks shut and open, but against the "base" of the relay), that causes the circuit board to flex upwards slightly, maybe 1/32" to 1/16", and bingo, everything starts working as it should: The Taco pump comes on, the zone valves open, the electrical readings are as you say they should be.

As a kludge, I have gently wedged a little dowel between the housing of the aquastat and the relay, to keep the circuit board "propped up", until it can be replaced.
 
  #7  
Old 01-22-15, 10:07 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,538
Likes: 0
Received 8 Likes on 6 Posts
What you've got going on there is not a 'short circuit' but rather a CRACKED SOLDER JOINT.

It's very common actually, especially with the newer aquastats that were manufactured 'over the border' and using the lead free solder.

That could be easily repaired by someone that knows how to solder.
 
  #8  
Old 01-24-15, 07:15 AM
T
Member
Thread Starter
Join Date: Apr 2011
Location: USA
Posts: 67
Likes: 0
Received 0 Likes on 0 Posts
Again, thank you for the info.

If at all possible, I'd like to do it myself, since the minimum charge for a home visit around here is about $200, and the heating company is even likely to say that they don't repair circuitboards and will want to sell me a new one, so the cost will end up between $500-$700, which I'd rather spend on heating oil.

Would I be looking for something like this picture found on the internet?
 
  #9  
Old 01-24-15, 08:08 AM
Geochurchi's Avatar
Member
Join Date: Nov 2012
Posts: 5,617
Received 157 Likes on 143 Posts
Exactly,really easy to repair.
This could work fine,check You Tube for soldering tips
http://t.homedepot.com/p/Weller-25-W...KUS/204195328/
Geo
 

Last edited by Geochurchi; 01-24-15 at 08:15 AM. Reason: Add link
  #10  
Old 01-24-15, 09:48 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,538
Likes: 0
Received 8 Likes on 6 Posts
Make sure to use solder for ELECTRONICS, which has a non-acid flux in the core. Solder sold for plumbing will have an ACID core.

It would be best to first remove the old solder by use of "Solder braid" which wicks the molten solder up. Then apply new solder. I didn't look at the video, they may have covered that part.
 
  #11  
Old 01-26-15, 09:25 AM
G
Member
Join Date: Mar 2014
Posts: 57
Received 0 Likes on 0 Posts
i had a similar issue with my Honeywell 8148, only worked when the circuit board was gently pushed in by a small piece of paper wedged in the corner. Ended up replacing the aquastat under a service contract. And thank you for using a meaningful subject line, and not "heating/water issue"

Good luck.
 
  #12  
Old 01-28-15, 08:18 AM
T
Member
Thread Starter
Join Date: Apr 2011
Location: USA
Posts: 67
Likes: 0
Received 0 Likes on 0 Posts
My little dowel kludge has not proven to be perfectly reliable. The circulator cut off again last night, and I had to wiggle the dowel and open the relay manually to get things going again. Maybe it's time to solder.

I bought the braid to wick the old solder away, a new soldering iron (25W-40W), the right resin-core solder for electronics, and have watched several YouTube videos on soldering, and it's something I could probably do.

But how to remove the circuit board (after cutting the electrical supply)? I see there are little metal clips on the housing that have to be bent back out of the way. Will the circuit board simply lift up and out once those clips are bent out of the way? Or do I also have to let the boiler become completely cool and loosen the retaining nut for the sensor tube? Do the board and the sensor tube come out "as a piece"?Name:  DSCN3335.jpg
Views: 1905
Size:  34.7 KB
 
  #13  
Old 01-28-15, 08:37 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,538
Likes: 0
Received 8 Likes on 6 Posts
You'll have to bend those tabs to remove the board.

First though, you'll need to remove the cable connectors because they're in the way of removing the board. Leave the connectors on the ends of the cables and remove the locknuts and pull them out along with the cable.

Please make sure you label the wires! and a good idea to take some pics for reference.

The temperature sensing bulb comes out the back of the board. This will slide out of the 'well' into which it is inserted. BE CAREFUL that you do not 'kink' that capillary tube! It is NOT a wire, but actually a tube with 'stuff' inside. If you kink the tube, it's junk.

You might find it easier to remove the entire aquastat and take the board out on the workbench. There is a single clamp screw that holds the a'stat to the end of the well spud. Loosen but do not remove that screw. You need to loosen it enough that you can push the end of the screw which will lift the clamp so it can slide off the spud.

Pull straight out and don't stress that tubing...

Sounds more complicated than it is.

If you find one cracked joint, resolder them all.
 
  #14  
Old 02-13-15, 07:26 AM
T
Member
Thread Starter
Join Date: Apr 2011
Location: USA
Posts: 67
Likes: 0
Received 0 Likes on 0 Posts
It's been a busy two weeks, but I wanted to stop back in and say thanks very much for the help. The soldering worked, and the radiators are warmer than they've ever been. The aquastat must have been malfunctioning from day one. Now the electrical readings are good.
 
  #15  
Old 02-13-15, 08:41 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,538
Likes: 0
Received 8 Likes on 6 Posts
Good news!

Thanks for letting us know...
 
 

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