No heat or hot water? Big problem. Your boiler might be acting up. Check the thermostat; it's like the boss telling the boiler what to do. If it's off, that's a clue.
If your heat plant isn't warming up as it should, the problem might be with the gas valve. The first thing to do is find out what's wrong. Keep an eye out for signs like no heat, strange smells, or a pilot light that's yellow. These things can show there's a problem with the gas valve. Don't worry, we're here to help you figure it out and get your heat plant working again.