dpagini - Honeywell Aquastat L8148b Relay Fixable(powerpile)

Sorry to reply to an old thread,


http://www.doityourself.com/forum/bo...y-fixable.html


but I think I have a similar situation, and it's definitely involving the same product...

I have the same "aquastat relay L8148B" as the original poster. My thermostat kicks on at the boiler reliably when the house is below temp. I can "hear power" going to the circulator, and when testing the circulator connection (at the aquastat) with a voltage tester, the light comes on, so I'm fairly confident this is working.
My pilot is lit. There seems to be trouble with the gas valve either getting the signal from the aquastat to open, or possibly the pilot thermocouple...? Do you know of any reliable way to test either of these two possibilities? Can I manually send a signal to the gas valve to open (which would prove the thermocouple was working properly if it fires)...? I would hate to buy the replacement aquastat only to find out there is a problem at the gas valve. If my aquastat is bad and I needed to get a new one, I was actually replying to this thread b/c of the warning to the previous poster's gas valve type and the compatibility with the replacement aquastat.

Thanks in advance for any advice you could give me.

 

Isn't there an "AUTO / MAN " slide switch on the aquastat?

Do you own a multimeter and know how to use it?

Please advise full make and model of boiler system and the model of the gas valve if you can find it.

 

I will follow up with more details (when I get home), but here is what I have on hand...

There is an auto/man switch. What does this do exactly? If I switch to MAN, nothing different happens.

The boiler is a Burnham American ANS Z21-13 Low Pressure Boiler, stamped as 1977, Boiler No "P4-W-22AN". The Aquastat Relay is TYPE L8148B. Attached are a few photos of my boiler and info...

I own a piece of junk multimeter and can't say I'm very well versed in using it. I plan to attack this problem with my father's help, and has better equipment and is much more adept at using it. I guess I'm just now reading the photo of the aquastat... should I be testing the b1/b2 terminals for .25 amps?

 

Systems with what are called 'millivolt gas valves' (as I believe yours is) are capable of running the burner in the absence of 120VAC power. Switching the switch from auto to man should cause the burner to fire.

If the burner does not light, this could be a number of things at fault.

The switch in the aquastat could be dirty, the ThermoPILE (NOTE, this is a DIFFERENT DEVICE than a ThermoCOUPLE) could be defective, the gas valve could be defective, there could be corroded wiring connections between the thermopile and the gas valve.

No... that .25 A number is the maximum rating of the contacts, not what you will measure on them.

If you don't have the manual for your boiler, see if you can google to find one... when and if you do, come back here and post a link as to where you found it so I can take a look also.

 

Could not find a manual online, but I did discover my manual in my basement near my furnace. Is there anything I can take pictures of, or look for in there, that may help? I found the model of the gas valve... VS 820 A 1013

I will certainly call an expert in if I need it... my thought was that I could test some basic components of the unit to try and pinpoint what the problem was, but maybe it's not that easy as I'm thinking it is. Let me know if you need any details out of the manual... thanks!

 

That is 100% a '750 millivolt' gas valve.

Is there a troubleshooting section in the manual that describes how to measure the voltage of the "ThermoPile" or "PowerPile" (could be called either name).

If so read through that and see how you feel about tackling that.

It's very possible that this is your problem, and changing the part should not be too difficult.

 

I'm thinking the attached image is the page I'm looking for. It was actually circled in the book, which is definitely reinforcing my thought that this is the correct diagram. The page mentions the L8148B Aquastat. I also see mention of the Powerpile. What is the difference between a powerpile and thermocouple? I guess what I thought the thermocouple was, actually looks like the powerpile...

So this is likely my primary suspect for my troubles? Is there an easy way to bipass the powerpile and see if the boiler fires up to indicate that the powerpile may be defective?

Again, thank you a million times for all your help.

Edit: changing orientation of photo

 

Both devices output small voltages when they are heated. The main difference between a thermocouple and a thermopile is the magnitude of voltage.

Thermocouple might typically be between say 25 and 75 millivolts or so... ballpark figure.

ThermoPILE ( is actually a pile of thermocouples! ) output voltage is around 750 millivolts (3/4 of a volt...).

It would be the first thing I would test, a fairly common failure mode.

No way to bypass the pile... it's output voltage is what actually powers the gas valve. If it's not outputting enough voltage, the valve won't open. It's also a safety device that needs to be heated by the pilot flame. If pilot flame goes out for any reason, pile cools down, gas valve won't open.

What you CAN do is TEST the pile voltage with your multimeter. Set the meter to read DC volts, if your meter has different scales, set it to the lowest scale for say 1 or 2 volts... touch meter leads to the " PP " terminals on the gas valve. You should read right around 0.75 Volts ( which is 750 millivolts).

 

Ok, I think this is my culprit...

Just for the sake of being thorough, the steps I took... The pilot light was out. I decided to test before I lit it to give me a "control" I guess... I set the multimeter to DCV, and pressed the "range" button a few times, which seemed to move the decimal point... when the decimal was all the way to the left (3 numbers to the right) I figured this was the setting I wanted. I tested the the cold PP leads, and got the expected output of around .000. I then lit the pilot... waited a few minutes, and tested again. The highest reading I got was .100 (seen in photo below), or what I'm assuming is 100 millivolts, does that sound right? Would the powerpile be likely to output some volts, but just not enough to open the valve? Given this info, does it sound like I need to replace the powerpile?

Any suggestions on the replacement for this? I tried searching for "VS 820 A 1013" and "powerpile" and am not getting the results I think I need...

 

Yes, that's 100 millivolts... 0.100V .

What do you read if you lift one of the powerpile leads? and measure at the free wire? Same?

It may take a while to bring a fully cold pile up to max output, but my impression is that yours is low.

Isn't there a parts list in the back of the boiler manual?

 

K... so I went home tonight and the pilot was out again. I lit it back up, read the leads again. 0.000 without the pilot lit, right around 0.100 when I first lit the pilot. Then I waited about 5 minutes and was getting a reading of 0.108. Then I waited about 20 more minutes, and read it again, and was getting around 0.084. Odd, but it seems like this is definitely a problem.

I wasnt sure exactly what you mean by "what do you read if you lift one of the powerpile leads"...?
I tried putting the multimeter pins to the spade terminal instead of the screws and was getting the same reading. Is that sufficient? Or did you want me to unscrew and disconnect the powerpile wires? Do you think the checks I did are sufficient? Like I said, I did order the part, so hopefully Friday I can get it in and see if that helps me out...

Found a part... Q313A1022 and ordered it from Patriot Supply. We'll see how this goes.

 

It sounds like that's the culprit...

Yes, that's what I meant, but I really don't think you will see anything different... just curious was all.

 

closed that old thread and moved this to its own... Hope ya all dont mind....Put a link to the old in the OP's original post #1

 

No problem Mike... kept meaning to do that myself and got sidetracked.

 

Well NJ Trooper, I think I'm all set and running now and just want to thank you 1000x!!! When I pulled the old powerpile out, it had a huge hole blown out of the side and was definitely the culprit. Let me tell you though, that thing was a pain to change. The boiler is so old there was so much corrosion, and the bracket to hold the pilot and powerpile was such a tight fit between the burners.

Anyways, I have one final question for you... while I was completing the repairs to the furnace, I found a bunch of practically disintegrating insulation. There was a piece below the burners, maybe 1/4 to 1/2 inch thick, with aluminum foil on top of it. Also, on the access panel to the burners, there was another piece. Both of these pieces basically fell apart to the touch. HOw important are these two pieces of insulation to replace? What can I use to replace them? I called a plumbing supply store, and although extremely expensive, they recommended Kaowool. My father thinks I can just use fiberglass insulation with some aluminum foil on top, but the guy at home depot said that might melt. I don't totally trust anyone's opinion just yet, so thought I would get that last question in there... what do you think? Can I fire the furnace w/o that insulation? If I need it, what should I go with?

 

Is the boiler on concrete floor?

I'm would say to go ahead and fire it up if I wasn't such a worry wart. Something bad happens and I get blamed for it...

Go to Patriot Supply - Industrial, Commercial & Residential HVAC Parts & Equipment and type KAOWOOL into the search box. You'll get about 80 hits... on the last page you will see some kaowool boards. The #1028 is a 3' x 2' x 1/4" piece for about $30 or so... I bet that's more than you need.

The aluminum foil could be layed on top if you want.

You probably don't really NEED the piece below the burners, but the cover door might not be a bad idea.

 

It's on bricks, which are then on a concrete door. I will go ahead and purchase the kaowool boards you recommend, but for the sake of my freezing cold girlfriend, I might have to risk it and fire it up until those come in. Thanks again.

What a mess this boiler is... I actually removed the rusted screws that hold on the cover door on and replaced them with some new stainless hardware. There was only one screw holding the door in place as it appears the other screw broke off years ago. When I put the new screws in, the cover door did not align to both screws. Ugh. Glad this is almost over....

 

It's not like yer gonna burn the place down...

If there's any wiring or anything that touches the cover door, move it out of the way just so you don't melt stuff if the cover gets too hot.