The float could be stuck because of stuck needle valve, or rust. The float could also be leaking and be full of fuel.
Gonna have to pull the head and find out what's wrong. Could be a bent valve.
Your trumpet valve sticks because it is to dry if you want to fix it buy some valve oil undo the valves and put some along the metal piece.
Take the head off and replace BOTH valves.
You replace the gas valve.
Unscrew the cap on the top of the valve and pull out the valve. Make sure it is clean and apply valve oil to the valve. Depending on how stuck it is and if the euphonium has not been played in a long time will determine how much valve oil you will have to use. After you have oiled the valve put the valve back in, making sure the guide is lined up, and then screw back on the top cap finger tight. If the valve is really stuck and you can not get it out you should take the euphonium to a instrument repair shop so you don't damage the instrument.
If your main gas valve is stuck in the closed position, it must be replaced. This condition is the reason your thermostat will not cause the main burners to light.
It is just stuck,
odds are if the valve is stuck open it is either bent(from over rev/valve float), or siezed in the guide(over heating). no easy fix sry
Sounds like you bent the valve. You'll have to pull the head to fix it.
A code 37 on a Jaguar XJ6 means either your EGR solenoid or EGR valve is bad. Most of the time the valve is simply stuck open and it is a very easy fix.
The valve has failed.The valve has failed.