Dual Fuel Boiler Problems

I have a newer Dual Fuel system (2 years old) with a Thermolec 20 Kw boiler as the main boiler and a propane bolier as backup.

Just recently the electric boiler started acting up. It works fine when the zones call for heat but once the heat requirements are satisfied and the boiler shuts down the temp guage on the boiler starts to rise slowly until it hits 180 degrees then the thermal overload will shut it off.

Some how the elements are still heating when it is not calling for heat.

I have a tech working on the problem. He has changed the 2 Magnetic Contactors and now says it is the Relays or a bad element.

Just wondering if any one out there has had any problems similar to this?

I could be a relay.

But, If the element was bad then it would not heat.
The only way a bad element would overheat would be if the unit was wired so that the relay switches the neutral and not the hot.