Weil McLain GV 4 Series 2 Constantly On & Off

Docfletcher

At this time were only using the boiler for the indirect water heater. The boiler goes though it's start sequence, fires up, stays fired up for a minute or so and shuts down. Then within 30 seconds or so does the same thing all over again. No errors on the GCM. The possible could be's that come to mind are... 1. Bad Hi/Lo Limit. 2. The gas valve itself (you can hear the pop'et valve actually close with a stethoscope, turn off in two clicks 1/2 second apart. 3. Not enough water flow through boiler. 4. Bad air pressure switch, and lastly perhaps a block temp switch is bad. So I'd appreciate your help and advice on what should be explored, checked first. Thanks.

Empire_2

You have a good start on your potential problems. Do you think it has flow thru the boiler? Is pressure @ 12psi or so? I don't think it's a flame sensing problem since it clearly proves after 4 sec or so. Yea, it might be the Aquastat doing its thing, but since there is little or no flow maybe that's something you can look at.

Peace;
Mike T.

Docfletcher

Fired it up from dead cold. Stayed lit till 140 then shut down. I suspect limit control. I will prove it out when I get home.

Docfletcher

Connected the limit assembly wires to an old limit unit I had tucked away. Still have the same problem so I think that rules out the limit assembly. Also ruled out insufficient water flow and the block temp switch. So the long and short of it is... I don't know. Back to square one.

Empire_2

You might want to check to manifold gas pressure and see what it's doing. If it's dropping out, check the incoming to see if there is a possible meter problem. Break out the meter and start checking the main valve, and any other safety's.

Let me know what you find.

Mike T.

Docfletcher

I think the air pressure switch is opening up, dropping the 24V. That would send a no air signal to the GPC shutting things down fast. I have not verified it. I gave the switch a good soaking with DetoxIT D5 and the problem is gone, at least for now. I do not have a man o meter so I can't be sure if I have 1.4wc. But I checked air hoses and they are in good shape. I'll replace the pressure switch and see if the problem goes away. It's cheep enough at $35 and the current one is 21 years old anyway. Thanks for chiming in Mike. I really appreciate it.

Matt_67

Had a situation like that where a bad end switch on a zone valve was cycling the boiler. Is the pump turning off along with the burner?

Docfletcher

The indirect water heater circulator stayed on when the boiler shut down because it was calling for heat. I'm not sure if the boiler circulator itself was off. I didn't pay attention to it, but since you mention it I wish I did.

Jason_13

Is this a new boiler or one that has been in for awhile and this is a new problem.

Docfletcher

21 years old. New problem. However it's appears to be resolved now. Have to give it some time to be sure. I hate the thought of another a winter with this boiler.

Empire_2

Just a little FYI, Never clean parts like you stated! You have just compromised the integrity of the switch. This is a safety switch and submerging it in water renders the control useless... These parts are NEVER to be put in water as the can become useless and not work as intended. Please,.....NEVER, clean any mechanical operating control in water. "It Can Kill YOU". If you do not have to meters to properly check the operation of the system, call in the professionals. Remember misfired boilers can kill you. I don't mean to keep restating it but, when you wash a safety control,....It concerns me.

Peace;

Mike T.

Docfletcher

Mike, Where did you get the idea I used water? I used a product called DetoxIT D5, it's an electrical parts cleaner made specifically for the purpose. I also ordered a new switch. Peace, Don

Empire_2

My bad. Just assumed and you know what they say when you assume.....lol.

Mike T.

Docfletcher

No problem Mike. Thanks.

Docfletcher

Boiler was working normally until I installed the new air pressure switch. Then immediately the problem returned. Here is a recap of the symptoms when calling for heat.
Nominal boiler water temp is 140F

GCM: Green to purge to ignite to valve, and boiler burner comes on. .
Zone 1 circ on and boiler circ on.
At 145 boiler shuts down, so does the blower instantly. GCM green.
Zone 1 circ and boiler circ on are still on.
About 30 seconds latter the cycle repeats itself.

It seems with each cycle the water temp goes higher. But, the cadence of the cycles never changes.
So I have about 2 minutes of up time and then shut down = Short cycles.
So back to the trouble shooting charts for me. Thanks in advance for any help you can give.

Docfletcher

The WM trouble shooting charts did not take me anywhere new so I'm not sure where to go next. maybe a call to WM? I jumpered out the new air switch and the problem remained, so put the old pressure switch back in. I checked the tubing , and probed the blower barbs looking for gunk and they are clear. No condensate in the clear box the tubes go in. I removed the GPM and gave it a wash with a true circuit board cleaner and cleaned all the harness contacts. Low & behold the boiler came back to life. It's like it never happened. I'm not sure if it's a good fix. Only time will tell.

BobC

Did they use molex connectors on the end of those harnesses?

Bob

Docfletcher

Not sure if molex or amp. But is the molex style. Pin into pin. Here's photo.

Docfletcher

Better shot.

BobC

Molex style connectors can be a real pita if the manufacturer cheaped out by using tin plated pins and sockets; they have poor resistance to corrosion.

Bob

Docfletcher

I looked closely at those pins, they were plated but the plating is gone so they have that cold grayish/whitish appearance. Boiler was fine overnight. Will see what happens when when it fires up.

BobC

We started using Molex connectors back in the early 80's and learned the extra cost of using a bronze phosphor pin and socket was well worth it from a reliability point of view. Up until that time we produced mostly military gear and used canon connectors with gold plated contacts, expensive but absolutely bullet proof.

Companies really shoot themselves in the foot when they allow the bean counters to dictate component selection based on cost alone. They know the cost of everything and don't understand the concept of value.

Bob

Docfletcher

Your last paragraph is very true. I'll never understand why they do like they do . They don't seem to care much about serviceability either.

OK, so here is what I found when I got into it a little deeper. I'm finally confident of what the problem is. I feel good about the temporary fix as well. It is the air switch dropping the 24v, but not because it's bad. The bug is at the GPU P3 connector pins where the air switch gets it's 24v. Those pins are not making a stable connection. I placed a wedge through the connector at each of the two red 24v wires forcing a good mechanical
connection.

BobC

If it were on my own boiler I'd just splice a wire from the connector solder pad on the board to the wire on the cable.

Bob

Docfletcher

Thanks Bob I will do just that, it's an excellent idea. I like it.

BobC

I checked the cost of molex pins on mouser.com. I didn't see bronze phosphor listed but they did list 30um gold. The tin plated contacts are $0.17 ea while the gold plated ones are $0.39 each.If there were 20 connections we are talking almost $9 extra (20 male plus 20 female X 22 cents per). The bronze pins would be someplace in the middle costwise.

$9 against a $2,500 boiler, bean counters at work.

Bob

Docfletcher

This GPU is getting tired. I already have a couple of repairs on it that were done abut 7 years ago. Jumper'ed the circuit path in 2 places on the underside.

Docfletcher

I've ordered the harness. It's a better way to go (PN 591-391-820). It's cheep enough I'll bet the GPU gets blamed for allot for the sins of the harness. Could be 3 weeks till the harness comes so for now I ended up putting nails in every topside P3 connector pin as the two I had on it were not enough. Looks goofy, but really does the job for now.

BobC

When you get that harness check the solder joints on the board to be sure you don't have any cracked solder joints around the molex pins.

It might be worth using some Caig Deoxit on the pins before putting the new harness in.

Bob

Docfletcher

Hi Bob, Yeah the DeoxIT D5 is what I have on hand. The bottom part of the connector is solid, pushing it in any direction no longer causes a problem. That makes me confident the issue is simply the upper part of the connector. Here's the nails photo, as far as I could tell all points were bad except the ground, but I nailed it also anyway. I taped the nail head areas to prevent shorting.

BobC

I've done similar temp repairs using the wooden shafts of Qtips.

Another thing to watch out for pins being crimped on unstripped wires, it works fine initially until the crimp loosens just a little bit. I've also run into the same type of problem with ring lugs (on Northrup Grumman equipment - I hope they take a little more care with the aircraft).

Bob

Docfletcher

I'll be sure to take that connector apart latter just for grins. Maybe I'll find something definitive like the crimping unstripped wires you speak of. It was a pretty good bug, having me going in circles for a while. Those wooden Q tips are kinda scarce these days. I would not have thought to use them anyway. I fall back to methods I used before I retired.

Ring lugs, I dislike them for most applications. I much prefer the spade type, easy on easy off. IBM stuff used allot of both types on their stuff.

BobC

We used the wooden Puritan Qtips to clean ckt boards, they were almost 6" long with a maple shaft. I bought some for my own use a few years ago from Cabela's where they sold as gun cleaning accessories.

Bob

Abracadabra

BobC said:

I've done similar temp repairs using the wooden shafts of Qtips.

Another thing to watch out for pins being crimped on unstripped wires, it works fine initially until the crimp loosens just a little bit. I've also run into the same type of problem with ring lugs (on Northrup Grumman equipment - I hope they take a little more care with the aircraft).

Bob

Northrop.. not Northrup.. Northrup is the seed company.. was an ongoing joke when I worked there

Docfletcher

I remember those 6" Q tips now, ours came in a white paper bag. 50 or 100 can't really remember. We cleaned some things with trichlorethylene. Not good for you stuff. I used alcohol whenever I thought it would do the job.

rick in Alaska

I had the same molex issue on a furnace. Drove me nuts trying to figure out the problem. I wound up using wooden toothpicks on mine to see if it was the problem. It worked a while then quit again. We finally change out the circuit board and it has been fault free for months now. I never found any issues with the board as far as bad solder joints, but it must have been.
Rick

Docfletcher

Hi Rick, I think the wooden toothpicks might have a bit of give, over time they may expand and contract due to moisture and temperature and may loosen up. Steel on the other hand stays tight and the point actually connects to the top of the metal connector where it's crimped. It could be 3 weeks before my harness ships. I'm fairly sure the nails will hold up in the meanwhile.

Docfletcher

New harness arriving today (Friday) but I don't think I'll be using it. I got tired of waiting for it so I took the control board out and re-soldered all the pins on the connector underside. Re-installed it, removed the nails from the upper half and it has been doing just fine. So I guess I'll eat a little crow here and say the board was the problem. I'm 100% sure the problem is gone. Famous last words.