'Auto' mode not working on Aquastat L8148J

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Old 02-28-09, 07:25 AM
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'Auto' mode not working on Aquastat L8148J

Hi,

I have a Honeywell Aquastat L8148J on a gas boiler. Recently, the 'Auto' mode stopped working. Everything else works fine when switched to 'Manual' mode, so I assume that all these components are fine:
Relay contacts for circulator
High Temp shutoff
Temperature probe
etc.

When in 'Auto' mode and the thermostate calls for heat, the relay closes and curculator pump starts and runs fine. However, the gas never switches on and the ignitor never ignites. Of course as soon as I switch it to 'Man', everthing works.

I did label and remove all the wires and try to see if there was any loose or corroded connections but I really could not get the thing apart. After putting all the wires back, the Auto mode started working and remained working for about 3 weeks. After that, I got Auto mode to work by tapping around the Aquastat with the base of a screwdriver. Now however, only 'Man' mode works. The mark on the high temp switch is '9436' which from other postings I take to mean it was made in week 36 of 1994.

Is it time to shell out $120 and replace the Aquastat unit or is there something clever which can be done. Or, is it in fact the Aquastat that is the problem?

Thank you,

Tim

ps - can pictures be uploaded to this site? or just links? thx
 
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Old 02-28-09, 09:25 AM
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Tim, it sounds as though the relay in the aquastat is not making contact to fire the gas valve... it could be dirty contacts on the relay, or a bad solder connection. I would try cleaning the contacts first with some 'contact cleaner'. Don't use abrasive papers on them... you will strip the plating from the contact and it will fail again sooner... use a piece of shirt cardboard soaked with the cleaner and hold tension on the contacts when you rub the cardboard between them. You can use isopropyl alcohol as a cleaner, should do the job.

From your description, I tend to think you have a bad solder connection though... and after you clean the contacts it may work for a while again because you have 'wiggled' the relay around and caused the bad connection to 'make' again.

To post pics, you need to upload them to a photo hosting site and provide a link here... you can set up a free account at Image hosting, free photo sharing & video sharing at Photobucket and upload there... drop a link to the album here.
 
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Old 02-28-09, 09:30 AM
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L8148j

Pictures are best done by posting on a photo sharing site such as photobuket.com & providing a link to them here.

What is the make & model of the boiler & gas valve? Is there a damper in the vent pipe?
 
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Old 02-28-09, 10:33 AM
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Hi Guys,

I'll work on getting pictures posted at photoBucket.

For now, I am looking at the schematic ==>
http://customer.honeywell.com/Techli...0s/60-2278.pdf ....in Figure 13 which shows that there is a capacitor in the circuit at the Man-Auto switch. I just wonder if this capacitor is bad or there is a loose/corroded connection. I can't tell which position of the switch (man or auto) goes uses the '1k2' capacitor but my guess is the auto position does.

I attempted to take the circuit board out of the box but since it wasnt coming out easily, I gave up. It kindof looked like some joints had to be un-soldered to release the board. What I need to see is on the back of that board and I dont really want to pull it apart until either, I have a replacement unit on site or Spring is here.

As for the relays being dirty, wouldnt the fact that with the switch in 'Manual' mode the boiler goes through all cycles perfectly and the:
burners light and
the circulator runs and
the high temp cut off works and
the low temp sensor works
indicate that the relay contacts are clean and working?

Thanks,

Tim
 
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Old 02-28-09, 10:54 AM
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Tim, the 1K1 and 1K2 are not capacitors, although if you are familiar with electronic schematics, they are drawn the same way. They are actually the RELAY CONTACTS. 1K is the relay coil.

The MAN-AUTO switch 'bypasses' the relay contact and fires up the burner. When you switch to MAN, and the thermostat is NOT calling for heat, you should not have the circulator running, only the burner.

The fact that switching to MAN is almost proof positive that the 1K2 relay contact is NOT 'making'.

Also, the 1K3 relay contacts are NOT in the circuit, because since you have a 'millivolt gas valve' the jumper from TP to Z must be removed.
 
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Old 02-28-09, 11:10 AM
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Millivolt gas valves

A bit about them:

The "POWERPILE" is the device that provides power for the gas valve to open. It's output is in the neighborhood of 750 millivolts. There is no power sourced FROM the aquastat to power the gas valve. When the contact is made in the aquastat, all that does is 'switch' to power from the powerpile to open the valve.

Since they work on relatively low voltages, if small resistances build up on the relay contacts due to oxidization, they can have a large affect on the operation of the valve.

If you have a voltmeter, measure the voltage output of your powerpile. It's _possible_ that it's output is low... and in that case, the resistance of the contact can put the valve on the 'borderline' of working/not working...

If the output is low, it could be a defective powerpile, or the pilot flame isn't heating it properly.

Just a few more things to confuse the issue...
 
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Old 03-01-09, 06:05 AM
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Hi Trooper,

Thanks for pointing out that '1K' on the schematic are relay contacts, my limited knowledge led me to think they were condensors. By cleaning them, I think that I may have eliminated them as a cause.

Since I heat mostly with wood, I had the boiler powered down for the last 2 days. This morning before powering it up, I sprayed 'contact cleaner' on the relay contacts. Then I slid a small strip of paper from a 3x5 card between the contacts and with some pressure on the contacts, I pulled the paper out. This I did several times.

Next, I turned on the power to the boiler (switch in Auto) and turned up one thermostat (call for heat). After 2 minutes, the relay clicked closed and the circulating pump started. When operating properly in Auto mode, there is a delay then the gas comes on and fires up, but now nothing happened. Then I started tapping things with the base of the screwdriver (still in Auto mode) - first the transformer..nothing happens, then the relay....nothing happens, finally I tap the brown high-limit switch and presto it fires up, but then dies after 30 seconds. I can continue to coax it to fire up by more tapping on the brown top of the high-limit switch but then it dies. Finally, not able to get it to heat up in Auto mode, I switch it to Manual and it heats up then shuts off, heats up shuts off etc.

Both Manual mode and Auto mode use the High-limit switch, so why does it work one way and not the other. Maybe my tapping on that side is moving some other component on the back of the circuit board and it just looks like the high-limit switch is causing the problem, a false lead so to speak.

As for the PowerPile not sure which part this is but I have a white block below the Aquastat that controls the igniter and the gas valve, is this the Powerpile? There are just 2 wires leading into this Powerpile and these 2 wires come from B1 + TV. Do I have it right that you are suggesting that I read the voltage across these 2 points (tv , b1), should they be disconnected from the Powerpile when I do this?

From all of the above, I am now thinking that the Auto/Man switch is bad or a connection from the switch to the High-limit switch is flaky.

Thank you,

Tim
 
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Old 03-01-09, 07:31 AM
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Tim, I be confused now...

The TV terminal should be connected to the thermostat or zone valve wiring... something isn't making sense here...

You need to get those pics up, and also please tell us what boiler model you have.

Oh yeah, remember that there are two and possibly three sets of contacts on that relay, only one of which controls the gas valve. Without knowing which set is for the valve, you need to clean them all...

The Auto/Man switch is good, and the fact that the burner fires properly when the switch is in the MAN position is telling us that the high limit control is OK too... there's either a problem with the relay contacts, or there's a bad connection at the point that the relay connects to the circuit.
 
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Old 03-03-09, 05:09 AM
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Phew, I am back, was pulled away by work and I am trying to be 'the best' employee now, considering that having a job is the best investment, I am trying to keep it.

So, anyway....here is a link to some pictures:
Pictures by ts_pictures - Photobucket

And, I double checked, the screw at the top left of the Aquastat (marked 'TV') has two wires a)goes to the zone valves/thermostat b)goes to the PowerPile/ignitor block. This latter one goes to a terminal marked '24v-gnd'.

-Tim
 
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Old 03-03-09, 05:15 AM
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Just a note, when you look at the pictures, it appears that the black wire from screw TV doesnt go to the PowerPile.

The picture is misleading because one black wire goes behind the other and it looks like TV goes to C1 but that is not the case.
 
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Old 03-03-09, 09:41 AM
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please tell us what boiler model you have
Can't look at the pics right now... will do later...
 
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Old 03-03-09, 03:03 PM
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OK, so it's a Hydrotherm... which model?

I'll tellya, looking at the pics I'm of the opinion that you've got a 'butchered' up system... is that module below the aquastat an S8610U ? I think that's what I see...

You do NOT have a 'powerpile'...

You do NOT have a millivolt gas valve...

Not sure what to tell you to do at this point. Your system needs some re-work...
 

Last edited by NJT; 03-03-09 at 03:43 PM.
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Old 03-03-09, 05:03 PM
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Hi Guys,

The boiler is a HydroTherm HC 145c-P 145k BTu.
The white box below the Aquastat is a Honeywell 'Universal Intermittant Pilot Module S8610U'.
S8610U

"APPLICATION
The S8610U Universal Replacement Ignition Module is designed to provide easy field replacement of a wide range of intermittent pilot ignition modules manufactured by
Honeywell, Robertshaw, Johnson and others. The S8610U
Module provides ignition sequence, flame monitoring, and
safety shutoff for intermittent pilot central furnaces, residential boilers, and other heating appliances."
 
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Old 03-03-09, 05:45 PM
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I didn't look at the link you posted, but I usually prefer to go right to the horses' mouth:

S8610U install sheet

This control needs to be properly GROUNDED to work as it should.

And, if you don't have the manual for your boiler, you might want to download and save the appropriate one of these...

HC-D , HC-E, R series
 
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Old 03-03-09, 05:54 PM
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This system has worked flawlessly in Auto mode for the last 10 years, now the Auto isnt working so I guess the Aquastat needs to be replaced .
 
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Old 03-04-09, 03:06 PM
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I printed off the installation manual and am reading it looking for clues, there is some troubleshooting flowcharts that might give me some clues. Thanks for the link.
 
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Old 03-04-09, 04:53 PM
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Here's the thing about your setup and wiring:

The 8610 module and gas valve that you have typically would not be wired such that the Auto/Man switch would have any effect at all. B2 is usually used for millivolt gas valves and that's why I thought you had one of those. Normally, the setup that you have would run off the 24VAC gas valve circuit... which would be terminal B3 ... but there's not even a screw in that terminal... which leads me to believe that at some point in the past someone did some 'creative' re-wiring on your system to get it to play... so before you do any repairs, you should first sit and figure out how it's currently wired and see what you can do to make it 'right'...

If you are able to sketch out a diagram for the way it currently is, I might be able to offer some suggestions...
 
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