Furnace partially working, but not quite... let's just say it's not.

Abit2chili

Jamie Hall said:

neilc said:

or, if you have 24v across T T then your endswitches(therm) is open

From t1 to t2 there is .087vac

Then your problem isn't with the end switches. 0.087 VAC is indicative of a closed circuit, which is what you want if the end switch is closed. The voltages from those terminals to ground is almost irrelevant -- it's amazing, but little appreciated, how varied the voltages in isolated wires can be in the presence of AC current (didn't used to be a problem, years ago -- you only had the problem with VTVMs with input impedance over 1 megohm -- anyone remember those besides me? Nowadays the big box multimeter has an input impedance that high -- and you can get some really wild results with them). Problem has to be either the control isn't switching -- or the thermopile or gas valve isn't behaving.

Are there certain readings that I should be looking for from the switch to valve and what is the switch controlled by? 

neilc

Abit2chili said:

.023vac

and 0.024 from your prior post,
these are both across V1 and V3, corrrect?

at the gas valve, pull one of the power pile wires off the valve,
you test between the wire, and the terminal, what's that voltage ?
you will need clips or a helper, the pilot will extinguish and you will need to relight, and let it warm up a minute or 2, then test,
you're looking for ~ 0.75 v / 750mv
pg2
https://s3.amazonaws.com/s3.supplyhouse.com/manuals/1249544894162/Honeywell-VS820-Product-Info.pdf

Abit2chili

neilc said:

.023vac

and 0.024 from your prior post, these are both across V1 and V3, corrrect? at the gas valve, pull one of the power pile wires off the valve, you test between the wire, and the terminal, what's that voltage ? you will need clips or a helper, the pilot will extinguish and you will need to relight, and let it warm up a minute or 2, then test, you're looking for ~ 0.75 v / 750mv pg2 https://s3.amazonaws.com/s3.supplyhouse.com/manuals/1249544894162/Honeywell-VS820-Product-Info.pdf

Correct .024vac

For the powerpile both leads from pp when I removed and tested from the wire to terminal it was .024vac

Jamie Hall

Abit2chili said:

Jamie Hall said:

neilc said:

or,
if you have 24v across T T then your endswitches(therm) is open

From t1 to t2 there is .087vacAre there certain readings that I should be looking for from the switch to valve and what is the switch controlled by? 

The end switch in the zone valve is mechanically controlled by the zone valve mechanism. When the zone valve is fully open, on that type of valve, the end switch terminals close and, if I recall correctly, the actuating element is de-energized (little hazy on that).

The centre terminal of the zone valve is, most often, common or ground -- but it can be wired so it is 24 VAC hot, and work just as well. Depends on how the rest of the system is wired. Remember that switches -- whether they are end switches, thermostats, dry relay contacts, whatever -- never supply power. Although they do is close a circuit from a power source through a load and back to the power source. And, presumably, the load does something useful! (as a sort of aside, I might add that solid state switches -- transistors, SCRs, Triacs and what have you -- have managed to confuse the issue mightily. They might seem to act as relays, but they don't, really, and dropping them into a circuit designed for relay dry contacts and isolated coils can have interesting (!) results).

pecmsg

Jamie Hall said:

(as a sort of aside, I might add that solid state switches -- transistors, SCRs, Triacs and what have you -- have managed to confuse the issue mightily. They might seem to act as relays, but they don't, really, and dropping them into a circuit designed for relay dry contacts and isolated coils can have interesting (!) results).

The biggest Issue with NEST is the backfeed across triacs . Sends signals to the computer that something "Is or Should be open and or closed!

ratio

The key to understating triacs/SCRs/etc. is to understand that they are unidirectional low resistance/high resistance devices at heart, not bidirectional open/closed devices. Low resistance/high resistance means that they must have a sufficient load attached to appear 'closed'. Unloaded –or underloaded– they appear to be 'open', you will see ≈input voltage on the output terminal. Unidirectional means that the devices that were used to build them conduct in only one direction—to carry AC, two devices are packaged together in one unit. A failure of one of these internal devices can results in a rectification of the output current when the package is in the off position. A magnetic device (contactor, motor, etc.) will complain about this by buzzing loudly & burning up.

neilc

Abit2chili said:

Are there certain readings that I should be looking for from the switch to valve and what is the switch controlled by?

the boiler controller switch for the thermopile gas valve circuit is controlled by,
A,
the call for heat,
your thermostat(s), which open your zone valves on 1 and 2,
and their end switch, 2 and 3, which complete the TT at the boiler control,
and B,
at the boiler control, the water temp, which you know is cold enough,
calling the circ, and the gas valve,

you know TT is made by the low, ~0v, differential across TT,
If TT was high, 24v, the issue would be back at the valves or thermostats,

and same idea at the boiler controller V1 V3,
I'm thinking your thermopile is shot and needs replacing,
it's not making enough voltage, not making 0.75v / 750mv.
you might try cleaning it, and relanding its wires,
everything is tight, correct?
and is the pilot clean blue and heating the pile well?

neilc

Abit2chili said:

.023vac

I missed this , , ,
the powerpile is dc, not ac,
measure again with the DC scale, wire to terminal at the gas valve.

remove the powerpile wire from one terminal at the gas valve,
test between the wire and the terminal,

Abit2chili

Okay, I will when I get back home later and let you know.

neilc

whachya buyin ?

Abit2chili

neilc said:

whachya buyin ?

 Some bad service and a mediocre meal it's Valentine's day 😄

EBEBRATT-Ed

Now we see that it has a power pile, that changes things a little.

Disconnect the wire from V3 Put your meter in series with the powerpile buy putting 1 meter lead on terminal V# on the control and the other meter lead on the powerpile wire removed from terminal V3.

Your looking for DC milli volts. The power pile puts out up to 750 mv I think. I forget the exact reading you need but if your down in the 300 or less it won't work. If your up around 500 it should.

That is with a good pilot flame which is burning against the power pile

The other thing to check is to shut the power off to the control and disconnect both wires from V1 & V3. Put your meter leads on V1 & V3 with the meter set to ohms . The circuit should be open with the power off and closed with tthe power on.

That proves (partly) that your control should start the burner

mattmia2

Is there another safety somewhere in the thermopile circuit? Is there something besides the valve, the thermopile, and the combination control in the thermopile circuit? Is the valve turned to "on" vs "pilot" if it is that type of gas valve? does anything other than the thermopile and the combination control connect to the valve? can you sow the schematic on the boiler if there is one?

Abit2chili

EBEBRATT-Ed said:

Now we see that it has a power pile, that changes things a little. Disconnect the wire from V3 Put your meter in series with the powerpile buy putting 1 meter lead on terminal V# on the control and the other meter lead on the powerpile wire removed from terminal V3. Your looking for DC milli volts. The power pile puts out up to 750 mv I think. I forget the exact reading you need but if your down in the 300 or less it won't work. If your up around 500 it should. That is with a good pilot flame which is burning against the power pile The other thing to check is to shut the power off to the control and disconnect both wires from V1 & V3. Put your meter leads on V1 & V3 with the meter set to ohms . The circuit should be open with the power off and closed with tthe power on. That proves (partly) that your control should start the burner

On v3 with the wire disconnected and the meter in series it is 228mV DC

From the red and white wire off the power pile it also has 228mv DC

V1 and v3 disconnected it has continuity or 0ohms with the power turned on or off

EBEBRATT-Ed

@Abit2chili

At 228 millivolts open circuit your powerpile is bad for sure. What happens is a new one will put out like 6-700 mv open circuit. When it powers the gas valve and puts a load on it the MV drops. I don't remember the voltages but 228 is bad for sure. You need like 300-350 minimum when powering the gas valve or it will not open

Abit2chili

@EBEBRATT-Ed
Does it matter that with v1 and v3 disconnected and testing the ohms it has no resistance with the power on or off?

HVACNUT

Forgive me if I'm wrong, but jumping didn't start the burners? Zone valves open and circulator running?
Boiler left off overnight in freezing temperatures? Frozen loops?

Abit2chili

HVACNUT said:

Forgive me if I'm wrong, but jumping didn't start the burners? Zone valves open and circulator running?
Boiler left off overnight in freezing temperatures? Frozen loops?

Valves are open, circulator is running. The basement never dropped below 50°F at night I have a thermostat down there and the rest of the house the thermostats read ~55°F.  I can still hear the water circulating in some of the baseboards in the house at times.

EBEBRATT-Ed

@Abit2chili

If you disconnect V1 & v3 and put your ohmmeter on those terminals with the control calling for heat the circuit should close, with the control not calling it should be open

Abit2chili

EBEBRATT-Ed said:

@Abit2chili If you disconnect V1 & v3 and put your ohmmeter on those terminals with the control calling for heat the circuit should close, with the control not calling it should be open

Okay now I understand, I will check when I get home. 

Would the low ~220mVdc reading from the power pile be an indicator that the power pile is dirty on the outside or possibly needing replacement?

mattmia2

Abit2chili said:

EBEBRATT-Ed said:

@Abit2chili

If you disconnect V1 & v3 and put your ohmmeter on those terminals with the control calling for heat the circuit should close, with the control not calling it should be open

Okay now I understand, I will check when I get home. 

Would the low ~220mVdc reading from the power pile be an indicator that the power pile is dirty on the outside or possibly needing replacement?

You need a new one. They degrade with time. It is a junction of dissimilar metals that produces a current when heated. It should measure shorted with an ohmmeter, but that isn't diagnostic, the current and voltage it produces when heated is how you tell if it is good or not. There is a small possibility it isn't enveloped by the pilot flame, but it is most likely just worn out.

Abit2chili

Replaced the thermopile and it is working now.
I want to thank everyone who helped me 👍 you guys are awesome!

EBEBRATT-Ed

@Abit2chili

Good show! glad you got it running. Took a while to get there!