Beckett R7184 reliability?

coldguy23

How common is it for one of these to fail, causing random or consistent burner startup issues?

And what usually goes bad in them?

Thanks!

Steamhead

Not common at all- but if there was a power surge, all bets are off.

Big Ed_4

They do go , it would be the last thing to change , until you find the issue . To find the issue you have see the glitch .

HVACNUT

What's the ohm reading when running?
Is there an oil delay valve and pre purge? 
If yes, is there post purge?
Does the burner go into safety?
Is TT jumped or is TT switched?

coldguy23

Steamhead said:

Not common at all- but if there was a power surge, all bets are off.

There have been many power surges over the years during high winds and rain, one prolonged outage, and a couple lightning strikes as well. I don't remember exactly if the lightning frying my TV coincided with the beginning of the sporadic failures, but it is possible.

Big Ed_4 said:

To find the issue you have see the glitch .

Yes that is the problem. AFAICT the glitch is simply the controller failing to provide power to the burner when it is supposed to. More on that below.

MikeAmann said:

Look at your burner's wear items first, and intermittent wiring problems.
Has the burner been serviced recently?

If by serviced you mean filters replaced (main fuel line canister, pump strainer, nozzle), igniter spark length checked, nozzle and electrodes cleaned and gapped... then yes. I'll check the wiring again but everything seems to be just as it was when the system was installed.

HVACNUT said:

What's the ohm reading when running?
Is there an oil delay valve and pre purge? 
If yes, is there post purge?
Does the burner go into safety?
Is TT jumped or is TT switched?

The ohm reading of the CAD cell during operation is 3 blinks of the LED, so between 800 and 1600Ω (4 blinks is above 1600 which is out of spec). I do not have the optional piece of equipment that would give me the exact reading. When checked while disconnected, it reads 4Ω when blasted directly with my 250lumen flashlight, 4KΩ in a well lit room, and OL when closed up in its housing in the dark.

This model does not have the delay valve or purges.

It never goes into safety/lockout, just randomly fails to initiate (I checked it with an ammeter on the wires going to the burner motor, igniter and solenoid to verify that it was not the burner that was failing to start).

The thermostat is not jumpered, but it has ~30VAC across the terminals whenever there is a call for heat so I have no reason to suspect it is bad. It is a NEST thermostat and the main blower responds instantly whenever it gets the heat call.

I have also already ruled out a bad high limit switch.



tyvm to everyone who responded!

HVACNUT

coldguy23 said: This model does not have the delay valve or purges. It never goes into safety/lockout, just randomly fails to initiate (I checked it with an ammeter on the wires going to the burner motor, igniter and solenoid to verify that it was not the burner that was failing to start). The thermostat is not jumpered, but it has ~30VAC across the terminals whenever there is a call for heat so I have no reason to suspect it is bad. It is a NEST thermostat and the main blower responds instantly whenever it gets the heat call. I have also already ruled out a bad high limit switch. tyvm to everyone who responded!

Not the thermostat (typo?) but is TT on the 7184 jumped? It should be if nothing is connected to it. But it's gotta be jumped or closed through some auxiliary otherwise it wouldn't run at all.

Is the NEST powered 24 volts (C is connected)?
Where is power for the NEST coming from, a switching relay, system transformer, dedicated transformer?

Does the fan start with the heat call or is there a delay?

coldguy23

HVACNUT said:

Not the thermostat (typo?) but is TT on the 7184 jumped? It should be if nothing is connected to it. But it's gotta be jumped or closed through some auxiliary otherwise it wouldn't run at all.

Is the NEST powered 24 volts (C is connected)?
Where is power for the NEST coming from, a switching relay, system transformer, dedicated transformer?

Does the fan start with the heat call or is there a delay?

TT is not jumped, TT has a yellow and blue wire coming from the control board's main wiring harness. Jumping TT starts up the ignition sequence every time, so I guess I have just ruled out the controller as the defective part.

The Nest is powered by the furnace control board (1158-110) and has a C wire. When the call for heat is initiated the white and green wires power up at the terminal block on the control board, so the thermostat is working as intended.

The main blower responds instantly whenever it gets the heat call.

HVACNUT

Ok, so that's something to check anyway.
When there's a call for heat, the reading should be 0 volts at TT on the primary. If it reads 24 volts, then it's not the primary. It's the board or something along the route of the yellow and blue wires between the board and TT.

EdTheHeaterMan

Does your furnace have a fan timer ST9103 that controls the system. the thermostat would connect to that control at the R W Y G C terminals. I have found that the ST9103 controls have a bad solder connection on the 12 pin plug where the orange wire from the R7184 connects.

When that happens the R7184 is working properly but the power from the Orange wire does not always get to the burner motor.

If you have that ST9103 fan timer, look at the back of that circuit board for any bad solder connections. You may want to replace it or repair the solder connection. Either way is fine.

coldguy23

Its an 1158-110, but you were correct, it was a cracked solder joint on one of the wiring harness pins. It was very hard to find since pressing my meter probe against the pin caused it to close. Decided the trace must be bad, removed the board fully and was going to solder a bypass when I finally saw it.

This seems to be a common issue. Why are these boards so susceptible to solder joints failing?

109A_5

Hello @coldguy23

coldguy23 said:

This seems to be a common issue. Why are these boards so susceptible to solder joints failing?

They are engineered to meet a price point and with a reasonable longevity (warranty period). They could be engineered so they to lasted longer with redundant or larger or different connections. That would cost more. And the HVAC community is quite comfortable just replacing the board or the whole unit if the board is no longer available.