Our tube is cracked and we can’t get a replacement until the morning. Can we run our boiler for the night with the tube off of the system and the valves closed off of either end of the glass tube?
The result is the same as running it while you are not there. There is no mechanical operation that would change the way the boiler operates if you close off the valves to the guage. But noone can tell you it is OK to operate it without seeing if water is in the boiler either; modern litiguous codes enter the decision.