If your oil or natural gas furnace is 12 years old or younger and has been properly maintained, you shouldn't worry about replacing your unit yet. Instead, you should spend some time and money improving energy efficiency in other areas of your home and ensure that your boiler is regularly and properly maintained so that it lasts longer. Simply put, if your boiler is more than 15 years old, you'll probably need to replace it sooner rather than later. Like any other major appliance, a boiler experiences great wear and tear.
To be clear, your boiler is heavily used, and it would be wise to replace the unit preventively before a major breakdown leaves you unheated when you need it most. Even if your boiler hasn't failed yet, older boilers will decrease its performance and efficiency, and can even be dangerous. In addition to age, there are other, more obvious signs that indicate that your boiler is too old. The standard pressure of a boiler should be between 18 and 21 psi.
If your boiler is operating at more than 21 psi, it could leak as a safety mechanism to prevent an explosion. However, sometimes sediment can build up inside the boiler, preventing the pressure valve from closing completely. To check if there is accumulated sediment in the pressure valve of your system, turn off the boiler and allow it to cool. Then, open the pressure valve and let the water flow into a bucket or bowl.
Inspect the water that comes out of the valve. Is that clear? If not, it is likely that you have accumulated sediment inside the tank. Doesn't the gas oven blow hot air? As with switches, someone may have closed a gas valve and then forgotten to turn it back on. Trace the gas line from the furnace to the meter and, if you see a handle that is perpendicular to the gas line, turn it so that it is parallel.
Gas oven repair depends on how old your oven is. If you have an old oven or boiler, it may have a pilot light. Remove the front panel and the burner cover and check that it is turned on. While it's probably best to leave the difficult problems of thermocouples, wiring, heat exchangers and fan motors to a qualified professional, there are a good number of things you can check before calling a qualified HVAC contractor for furnace repair service.
If you smell a propane leak, leave your home immediately and then call your propane supplier and a local HVAC contractor for emergency repair.