Ultra 230 series 1 E 18 lockout

LEADPIPE

This boiler is 17 years old and has given me no problems to this point. Yesterday I woke up to a cold house. When I checked the boiler I got the high temp lockout. Reset the boiler and it ran fine the rest of the day but locked out, same code. Changed the sensors, didn’t solve the problem. Verified the water temp with an infrared thermostat. The boiler will run the space heater zones IF the indirect HW zone is shut off. If I turn on the WH zone it will get priority and work fine. However, once it shuts down water isn’t being moved through the primary loop and the boiler will overheat and lock out. I pulled the thermostat wires for water heater and the boiler has been working “properly” for hours. There hasn’t been any work done to the system but I bled the system just to rule it out. I also noticed a type of shimmy coming from the IDHW tank before the boiler starts to heat up, almost like it’s fighting itself. Any ideas or suggestions?
Thanks!

HVACNUT

Is the indirect piped on the same manifolds as the space heat loop(s) or at the boiler, before the primary pump and separator Tee's?
You're description is a little confusing. You say the space heat will run if the indirect is shut off. 
Shut off how? At the aquastat, or physically turned off at the Ultra?
The indirect works fine and is priority, but when the indirect satisfies the boiler won't switch back to the primary pump for space heat?
What if you turn off priority? 
What is max limit and max firing rate?
Can you even set those parameters on a Series 1?

LEADPIPE

That’s because I’m confused
It’s not in the same manifold
Shut off at the aquastat.
Correct, the indirect works fine but once it’s finished the boiler will overheat.
I haven’t turned off priority
When it was installed it was oversized so I did turn down the fan speed. I’m sure you can adjust the firing rate, have to look at the manual.

I think it may be an issue in the Taco box. When I turned on the hot water zone, it came on but I didn’t get a zone light on the box. I think it’s something outside the boiler.

HVACNUT

You have a Taco zone panel. SR50?
Raise a heat thermostat then jump XX in the zone panel to see if the primary pump comes on. It should, along with the boiler for a space heat demand. If it does, the problem is the zone panel. If it doesn't, the problem is either a broken wire between XX and the connection at the boiler board, or the boiler board itself. 

LEADPIPE

I have the SR506. I disconnected the primary pump wiring from the boiler and connected it directly to a power source so it runs constantly and the boiler is running without any issues. I have someone coming on Monday but at least I have heat until then.