What are the dangers if a central heating system seizes up?

Not for sure what your asking try again.

The biggest danger is getting cold,, very cold, this could cause the immune system to get weak and makes it much easier to get sick,if one gets sick enough one could die.

Now,more info is needed as to what you are meaning (siezes up), are you talking about the motor? The compressor in a heastpump?
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