Weil-Mclain Ultra 3 blows 3 amp and Limit Open error

He surged the house.

I hate incompetent electricians (and other service people who do not know what they are doing, and do not even realize it).



N.B.: I am a home owner, not a heating technician. I do have an Ultra-3 however.



My guess would have been that you would need a new U-control and just try to get the former electrician to pay for it. And do not put the new one in until you find out what the trouble really is. The U-control has two fuses, a 3 Amp one and a 12 Amp one. One thing to check is that if you keep putting a 3 Amp fuse where the 12 Amp one should be, it is likely to blow. But do not put a 12 Amp fuse where the 3 Amp one should be.



"Troubleshooting on our own, we find that if we turn off the T-stat that

the boiler will display on, but we are in lockout mode - Limit Open.

The manual says check the jumper on the orange pins. It's set to

3&4."



Unless you have a safety device connected to pins 1&2 of the orange terminal block, they too should be jumpered. But neither 1&2 or 3&4 being absent should cause fuse blowing. Just no heat.



"It also says check wiring for external safety device. Could that be the

home surge protector? Before we got the protector we never got that

error."



No. The surge protector is not really a safety device, and if there were anything wrong with it, you would have problems in your entire house, not just the boiler.



"We would simply have the boiler on for a few minutes to a few hours

before it blew the fuse. the control module has been replaced. When

t-stat is on - it blows 3 amp. When t-stat is off, it doesn't blow but

we get limit open error."



I think you are going to need to get a really qualified heating service technician and a really good licensed electrician in there. It may be that the power panel, or just the surge protector, is wired wrong. I would not normally suspect this, but the fact that you had the U-control replaced and the new one has the same symptoms as the old one raises the possibility. Bad grounding? Hot and neutral reversed? etc.?



My guess is that the 3-Amp fuse just powers the 120 to 24 volt step-down transformer on the U-control board and that powers the electronics on the board. And my guess is that the 12-Amp fuse is what runs the (up to) three circulators.



I wonder if the surge harmed the thermostat and it is causing problems. Consider getting a box of 3 Amp fuses. Remove the thermostat and put in a new fuse. Turn the boiler back on. Not much should happen, but see if the fuse blows. My guess is that it will not. Then jumper the thermostat terminals (probably pins 1&2 of the RED P15 terminal block. This should simulate a call for heat. If it does and the fuse does not blow, you have a problem with the thermostat or the wiring to it. I do not think this is very likely, but you might as well check it. Fuses are way cheaper than U-control boards.



I also wonder about that 120 volt to 24 volt step-down transformer. If it is mounted on the U-control board, you will have replaced it at the same time as the U-control. But if it is separate, it may be defective (from the surge) as well. I do not know a good way of testing that without advanced equipment, but replacing it might be a smart move. I still think the best approach for you is to find a good technician who really knows Weil-McLain Ultra 3 boilers. When I was having trouble with this, due to some faults with the installation, W-M recommended my original installing contractor. I told them that and they recommended someone else who is better, but not ideal either. Their technician said I am their only residential customer with an Ultra 3 boiler. So we do a lot of mutual education. But at least they do not tell me that it is supposed to work like that, that gas boilers do not need annual maintenance, they now bring a digital combustion analyzer, all improvements over the former contractor.  Find a Contractor on this site may help you find one.