The answer to 'boiler freezing up' is that a frozen boiler is typically caused by a lack of water circulation or low water pressure in the system. This can happen when the water in the boiler or pipes freezes, blocking the flow. Common symptoms include the boiler not heating up, strange noises, or the system shutting down.
Some solutions include checking the boiler's water level and pressure, ensuring the thermostat is set properly, and inspecting for any blockages or leaks in the system. If you're comfortable doing basic troubleshooting, you may be able to fix a frozen boiler yourself by thawing the pipes or adding more water. However, if the issue persists or you're not confident in your ability to diagnose and repair the problem, it's best to call a professional HVAC technician to inspect and service the boiler.