Main burners will not light on gas boiler after gas valve replacement

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Old 08-28-14, 08:34 AM
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Main burners will not light on gas boiler after gas valve replacement

Hi Guys,

Would like to request assistance with a problem that has stumped me and the plumber. My mom and I both live in split ranch houses a few houses away from each other which have very, very similar nat gas heating systems (Hart & Crouse boilers circa 1960's, Honeywell t-stats, aquastats, relays, regulators, etc). My system had a leak in the pilot control so we had to change the entire gas control system out to a Honeywell VS820 A 1054 (a bit pricey) as replacement parts were no longer available. It worked out fine.
My mom's system over the last year or so experienced a situation where the main burner sometimes would not come on during the winter when she would turn up the t-stat. Long story short, the way to get it to activate was to tap on the gas valve lightly with a hammer and eventually the mains would kick in (I know). Figuring it was time to change out the gas valve, as maybe it was sticking, we replaced it with the same gas valve I installed (the VS820A, still pricey). When the pilot was lit, we raised the t-stat to call for heat and nothing (even tapping with a hammer did not help this time). The circulators would engage (1 for upstairs and 1 for downstairs) when we would turn up either t-stat.
What I know so far:
1) mV from my powerpile to my working gas valve (at both the TT and PP connections) with t-stat low= approx 353mV
2) mV from mom's powerpile to her non-working gas valve (at both the TT and PP connections) with t-stat low = approx 450mV
3) mV from my powerpile to my working gas valve at the PP connection with the t-stat calling for heat and the main burners firing = approx 153 mV and at the TT connection = approx 10mV
4) mV from mom's powerpile to her non-working gas valve at the PP and TT connections with the t-stat calling for heat and main burners not firing = approx 450mV (no change in mV when t-stat calling or not).
4) line voltage entering aquastat relay box on both systems approx 122V
5) both boilers pilot stays lit
6) the VS 820A valve says it is "Used in 750mV systems". Don't know if that means it must have a 750mV powerpile or the valve can be used in up to 750 mV systems. As such, both of our systems are below 750mV yet the one in which there is lower mV, the mains light and the system with higher voltage does not. The supply house that sold me the valve said the reason the mains are not lighting was because the PP was not putting out the required 750 to open the main valve, yet my 353mV PP lights my mains.
7) not sure if it happened or if it affects this issue, but my plumber tightened the piping to the outlet side of the valve real good. The install instructions mentioned that the piping should not be threaded into the valve more than 3/4in and max depth pipe can be inserted into control is 1/2in. He doesn't feel that it went in that far. The threads outside of the valve appear about the same that were showing with the old valve installed but I'm not 100% sure. As I said, don't know if it would therefore affect the mV readings that showed when the t-stat was raised to call for heat but it might affect the valve operation? Maybe? Or is something else electrically happening with the valve (new bur faulty?) or some other system component(s).
That's about it for now. Any thoughts on what to look at next would be GREATLY appreciated. Glad we started this before heating season starts here in MA. Thanks in advance for any help.
 
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Old 08-28-14, 10:27 AM
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Millivolt systems are generically called "750 millivolt" systems as this is the theoretical output of a typical power pile. The valves will generally operate down to quite a bit less voltage.

You said " T T " and " P P " but I think you mean " T H " and " P P ", don't you?

Where do the wires on the TH terminals go? Into the aquastat control? Trace those wires back and describe where they go.

(no change in mV when t-stat calling or not).
If by this you mean that the voltage at the TH terminals also stays the same, then this is telling us that the problem is NOT the gas valve... might not have ever been...

The fact that you see no voltage changes whether the t'stat is calling or not tells us that the heat call is not making it to the gas valve.

When that system calls for heat, the TH terminals are shorted together, by the aquastat relay, or other controls (there are several ways this could have been wired)

Does the aquastat on the boiler have an " AUTO / MAN " switch ? If so, what happens when you switch that to the " MAN " position ? (don't leave it there... switch back to AUTO when done)

Do you have a wiring diagram for the boiler that you can scan/photo and post?
 
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Old 09-01-14, 08:50 PM
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Yes, TH & PP! I am listing the first of what may probably be a few sets of photos of the system. Also, the aquastat does have an Auto/Man switch and I did switch it to Man but I did not leave it on very long to perhaps make the valve engage. I will try again. Anyway, it didn't light the main burners in Man when I switched to it even for a few seconds.
The wires from the TH terminals, in the photo, do go to the aquastat and connect to the B1 & B2 connections as can be seen in the aquastat schematic. The B2 terminal is connected to the gas valve TH connection where the PP white wire and the gas valve itself's red wire are also connected.
http://i105.photobucket.com/albums/m...ps405a1c06.jpg
http://i105.photobucket.com/albums/m...pse0e6b463.jpg
http://i105.photobucket.com/albums/m...pscb565424.jpg
 
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Old 09-03-14, 05:28 PM
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Any body have any thoughts from the photos and info? Thanks.
 
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Old 09-04-14, 04:10 PM
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Sorry for the delay Lou...

A little about how your system is supposed to work:

The power to open the gas valve is generated by the powerpile.

The aquastat terminals B1 and B2 are actually a 'switch' contact. When the system is called for heat, the relay component inside the aquastat closes and shorts those two terminals together, which completes the circuit from the powerpile to the coil of the gas valve.

So if you look at that, you can see that the aquastat B1 and B2 is connecting together (shorting) the two TH terminals on the gas valve.

The AUTO/MAN switch on the aquastat is wired ACROSS the B1 and B2 terminals.

When you switch to MAN what you are doing is closing the contact at B1 and B2, which is the same thing as shorting the two TH terminals together.

So, as a simple and quick test, you can take a piece of jumper wire and momentarily short the TH terminals on the gas valve.

If the burner fires, your problem is either a bad or loose wiring connection, broken wire, dirty contacts on the relay component in the aquastat.

If the burner does NOT fire, and you have voltage at the powerpile terminals, then the gas valve would seem to be the problem.

This test will at least tell you which direction you need to troubleshoot.
 
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Old 09-08-14, 01:22 PM
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Well finally found the problem and the main burners are igniting! Decided to do some more voltage and continuity testing to compare with my burner setup and started to think about some of the thermostat wiring that lay above the gas valve next to the aquastat (cannot photo since I unwrapped all the tape). The wiring had a lot of old cloth electrical tape wrapping the wires (which had begun to unwrap) and unused wires exposed around the tape ends (the wiring someone used was 3 wire and the t-stat only calls for 2). I decided to unwrap all this and see what was going on behind it all and maybe take some measurements there as well.
Surprise, surprise. The wiring ends were twisted together with no wire nuts to secure them (not even electrical tape wrapped around each paired end). The wires were all then scrunched up together and wrapped with electrical tape! I believe that several of the paired ends were probably shorting against each other or piercing into a nearby wire causing the problem of not allowing the electrical signal to travel correctly. Once all these wires were separated (but still paired), I decided to flick the electrical power swtich, t-stat calling, and the burners kicked on! Tried it a few times 'cause I couldn't believe the problem was a simple electrical connections(shoddy work from the plumber or electrician who wired this up so many years ago. Not secured correctly). The wires must have eventually made contact due to vibration from the system over many years and separating them solved the problem. I will be cutting, stripping, and reattaching the paired strands WITH wire nuts to hopefully make this a permanent fix. As it should've been. Just goes to show if you do it right the first time.... Thanks for all the help and will report back the final results when done cleaning up the mess. Unbelievable.
 
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Old 09-08-14, 01:26 PM
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Good deal Lou...

When you get that all done, go play some guitar and have a beer.
 
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Old 10-06-14, 09:58 PM
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Well, Murphy's Law struck again. So finally got around to correcting the shoddy wiring but too much time had gone by that I had a bit of trouble locating wires to the right terminals. I had drawn a diagram (should've taken photos) of what went where but I don't believe it was correct. So, some more info. The heat set up has one thermostat and circulator for the upstairs heat and the downstairs heat. There are (2) RA832A relays on the side of the boiler jacket for each floor as well. The RA 832A connections are where I'm a bit lost, now. I connected both upstairs and downstairs thermostats to each respective RA 832A relay's TT terminals. I believe the (2) relays' XX terminals should be wired in parallel. I am unsure, then were the L8084B aquastat 24V terminal connections need to go to on the RA832A. I've tried connecting them on the T and X terminals (hope I didn't damage any of the relays or other components), the T T terminals and the XX terminals and the problem is that....the main burners won't fire up! The same problem I had in the first place...again. So it worked when I untaped the shoddy wiring and when I clean up and re-wire, I don't get it right. I believe it's a wiring problem, still, but not sure what goes where on the 832. The other 832 has the t-stat wiring going to the T T terminals and the XX terminals are wired to the other 832, I'm deducting, that they should go to the XX terminals. Any thoughts on getting me back on track, if I haven't damaged anything with the 24V connections. Thanks very much.
 
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Old 10-09-14, 09:47 AM
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Using some schematic photos I found on the web of the 832 relay, I had the thermostats connected correctly but not the 24V wiring coming from the 8084 (they go to the XX terminals as do other circulator 24V wires in parallel). Once the wiring was correct, I started the system and got some V changes on the gas valve but not enough to open the valve. Again, I pulled on a few wires (why not, at this point) and, lo and behold, the burner came on! The wire connections from the B1 & B2 terminals to the Th & Th of the gas valve were intermittent signaling. I removed the wires at the aquastat, turned them around and reattached the wires and that did it. Just breaking the contacts. The V dropped to 50-80 mV from about 245 before the re-wiring thus opening the gas valve. If I tap on the aquastat on the side, though, the V changes 10-30 mV so the aqua may need changing (don't know if this is normal). The V changes didn't affect the gas valve opening, though. If the problem occurs again at least I know where the problem is. Otherwise, we're good to go! For now... Thanks for the help.
 
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