Excessive heating. If a boiler or self-fired pressure vessel accidentally suffers a general deficiency of water while working, severe damage may be caused to the boiler shell, firebox, etc. The risk is insurable as a whole or, in the case of a multi-tubular boiler, limited if desired to the overheating of the tubes only. The cover is for ‘self damage’ only and is put into effect as an extension of the boiler and pressure plant policy.