L8148E Aquastat Not Firing - No power from R to B1

homeowner1337

Hey folks, appreciate any help here for an experienced DIYer.

My boiler stopped firing yesterday. The relay is working, T & TV both have power and activate, the temp setting works and power flows from B to R. From there, it seems to stop though: I don't get any power from R to B1. I do not have a dampener, so the two terminals in the damper connection are jumped.

I've read the internal schematic here, and that indicates that there is no resistance between R and B1. As such I jumped the two externally with a wire and everything starts up correctly.

I've created a temporary bridge there (between R & B1) using the wire and some electric tape (not safe, I know, but temporary!), and that had my boiler running last night (see below pic).

My guess is the issue is a solder connection with the damper connection? Any other ideas or things I can test? If that's the case I'll have a pro come out and replace the Aquastat with a newer model (happy to take suggestions). Would love to know if there's anything else I can try.

Jamie Hall

Relay socket tight and clean connections? All other connections clean? Sounds like a problem on the board perhaps.

Big Ed_4

So you ran a jumper from R on the aquastat to B1 on the control bypassing the unused damper plug ? If correct , it sounds like the control is breaking down at the plug .. Since this is a boiler limit I would tell you to replace the control ....

homeowner1337

Big Ed_4 said:

So you ran a jumper from R on the aquastat to B1 on the control bypassing the unused damper plug ? If correct , it sounds like the control is breaking down at the plug .. Since this is a boiler limit I would tell you to replace the control ....

Yes, exactly. That's what it seems like to me as well. I haven't gone through and cleaned out the connections, but there don't really seem to be too many to clean (the wire off R is hot, and B1's connection works when I power at its base). Would love to take the board off and examine the other side, but at that point I might as well upgrade to a more efficient model

109A_5

Hello @homeowner1337,
It sounds like the Molex connector pin fitment is poor or a failed solder connections to the board.
A bit of disassembly, careful with the capillary tube and the bulb that goes into the well. The circuit board then comes out of the housing easily with the aquastat removed from the boiler.
Also while you are in there, a quite common failure is the solder joints at the at the relay go bad. They can be re-soldered and/or reinforced by cleaning off the old solder bending the pin(s) up enough to wrap a strand of thermostat wire securely around each pin and land it on the circuit board for about a 1/2 inch and solder it all. A fairly easy fix for an experienced DIYer with a soldering iron.

homeowner1337

@109A_5 thank you for that wiring diagram, I was looking for something that described the pin connectors!

From that, I'm wondering if the fuse blew. I took out the molex pin on 3 and moved it to 5 (which connects B1 and R directly in your diagram), and that worked like a charm! Thank you!!

109A_5

Hello @homeowner1337,
The diagram is from the link you posted, the 2nd last wiring diagram.
Yes, the fuse could have blown, but why ? An over-current event from a power surge, age related fatigue, other issues ?
With some research I think you will find the primary purpose of that Pico fuse is to intentionally blow when a motorized damper is added to the system. That way if the jumper was saved and if the damper fails closed the jumper can not be easily reinstalled and restore burner operation.
Secondary purpose, it is a fuse and it will protect the circuit from sustaining a lengthy over-current event. I would replace the fuse or put another (easy to replace) fuse in the circuit for further protection. I would guess that it is 3 Amps.

Big Ed_4

The fuse did not blow ... The burner is firing .

109A_5

Hello @Big Ed_4,

Big Ed_4 said:

The fuse did not blow ... The burner is firing .

You must have missed this...

homeowner1337 said:

From that, I'm wondering if the fuse blew. I took out the molex pin on 3 and moved it to 5 (which connects B1 and R directly in your diagram), and that worked like a charm! Thank you!!

Moving the one end of the jumper (from 3 to 5) bypassed the fuse found inside the Aquastat. With pin 2 to 3 the circuit goes through the fuse, with pin 2 to 5 the circuit bypasses the fuse.

To me the question now is; Why did the fuse blow or is it a poor solder connection at pin 3 of the connector. An Ohmmeter could easily verify the fuse.

homeowner1337

@109A_5 agreed. Fuse blew I think because of overloaded current. I accidentally shorted one of the lines after B1 (it's some sort of check in the back, below the flue). After that it wouldn't fire on its own

109A_5

Hello @homeowner1337,
OK, blocked vent / spill switch wire shorted to to the flue or boiler cabinet, that may do it depending on which side of the transformer is grounded.
If you have a S8600 type ignition module it may be hooked up backwards in relation to the Aquastat's B1, B2, see the wiring diagram above. Looks like Honeywell may have wanted B1 grounded (limit switches on the grounded side) to maybe avoid what happened to you. The boiler OEM wiring may be different.
Grounding something that is normally grounded usually does not blow fuses.

EdTheHeaterMan

109A_5 said:

Hello @homeowner1337,
The diagram is from the link you posted, the 2nd last wiring diagram.
Yes, the fuse could have blown, but why ? An over-current event from a power surge, age related fatigue, other issues ?
With some research I think you will find the primary purpose of that Pico fuse is to intentionally blow when a motorized damper is added to the system. That way if the jumper was saved and if the damper fails closed the jumper can not be easily reinstalled and restore burner operation.
Secondary purpose, it is a fuse and it will protect the circuit from sustaining a lengthy over-current event. I would replace the fuse or put another (easy to replace) fuse in the circuit for further protection. I would guess that it is 3 Amps.

Big Ed_4 said:

The fuse did not blow ... The burner is firing . Actually it did on purpose

The only reason for that fuse is to blow if a vent damper wire is installed on the damper socket, for the exact reason @109A_5 mentioned. You can't put the jumper back in to run the burner if the damper fails and get the burner to operate. I learned that over 25 years ago at a Honeywell seminar on vent damper equipped control modules. It is the only reason

There is no protecting from any overload, by that fuse. READ NOTE #3 on the diagram



If you look at the cable 197516A up close there are 5 wires connections but only 4 wires on the other end. If you do not have the cable then pin 3 and 5 stay connected and a jumper between pin 3 and 2 will operate the control. As soon as you connect a cable you can see a dead short ( @109A_5 Knows all about Shorts) from pin 4 to pin 3 thru the fuse to pin 5. This will make th jumper from pin 2 to 3 unusable in the future.

So, as long as that control is never connected to a cable 197516A, the fuse will never blow.

My guess is that the jumper moved from pin 2 to pin 5 is safe as long as the damper that was in line is removed, and that control or jumper plug is never salvaged and put on an appliance that has a closed damper in the vent.

So ...is that the original control and a damper was removed OR was that a salvaged control from a boiler that was damper equipped? Because I guarantee you that the control was connected to a cable with the pins 3 and 4 connected

homeowner1337

@109A_5 wow, I am amazed but you are right, it was wired backwards. B1 is connected to 24v, and B2 is connected to 24v GND. Can I just switch those? I guess I'd need to check that everything else is wired correctly.

Here's the wiring diagram from the ignition module, but I don't have the vent dampener part.

ronbugg

Looks like the ground wire was cut off the cable on the right. Wires in center are not in metal flex

Big Ed_4

There is no fuse in that control .....

109A_5

Hello @Big Ed_4

Big Ed_4 said:

There is no fuse in that control .....

Sure there is, at least in the OP's unit, you can see it in the picture.
Same as or similar to. https://www.digikey.com/en/products/detail/littelfuse-inc/0251003-MXL/700737

109A_5

Hello @homeowner1337,

homeowner1337 said:

Can I just switch those?

Maybe... Do you have the original boiler wiring diagram or an online version ? I would stay consistent with that, if it is available.

If all the rest of the 24VAC control system is 'floating' and not grounded any where else you could swap it to match the diagram posted first. Be advised it may violate Honeywells rules, even though they violate their own rules anyways. Look at the wiring diagram you just posted.


I believe the ground bonding is inside the Ignition Control Module, 24V GND bonded internally to GND (Burner) and then actually grounded at the pilot assembly.

Make sure there are no other grounds, you don't want both sides of the transformer grounded when all the controls close, something else may let go. Any doubt leave it as you originally found it.

Big Ed_4

Learn something every day , Thanks