Can a broken thermostat on an oil boiler cause hot water to flow out through the expansion pipe?
Yes, the water is getting too hot and is blowing out the pressure relief valve through the expansion tank. You should change this immediately.
I don't agree:
I am assuming that by expansion pipe, you are referring to the pipe
connected to the pressure relief valve - A broken Thermostat won't
cause the relief valve to activate. A broken thermostat will cause
the boiler to either run or not run as desired. However, a broken
(or incorrectly set) aquastat can cause the boiler to run too hot
and cause the valve to activate, but if it is chronic, it could be
a defective or dirty relief valve, defective expansion tank, a
problem with the pressure reducing valve on the domestic feed or
(as was my problem) an internal leak in my tankless coil.
What is your boiler's pressure gauge reading and what does the Temp
Gauge read on a call for heat (High Limit on and off)? Also, put a
bucket under the pipe and carefully burp the relief valve to clear
out any debris that might be causing the leak.
How do you know if your car thermostat is broken?
If the thermostat is broken in the closed position the engine would overheat rapidly. If it was broken in the open position the engine cooling system would not reach normal operating temperature and the heater would produce only warm air. Take the thermostat out and put it in a pan of water on the stove. When the water gets to around 200 deg F, the thermostat should open. If it doesn't it needs replaced. Observe…
What does it mean when the left side of your radiator was smoking and it damaged the radiator cap when you took it off there was a lot of coolant in the radiator?
Your water pump might be broken or your thermostat might need to be replaced. You obviously don't have a leak so somehow the fluid isn't moving through the engine. If the thermostat is broken it will not let fluid into the engine and then the engine will overheat and the radiator will release smoke.
What can a broken thermostat in a vehicle do?
In very short: If the thermostat stays open, the warm-up time for the engine will be significantly longer, resulting in unwanted start-up wear. If the thermostat stays closed, the engine coolant can not circulate through the engine and cooling system, resulting in the engine overheating, as the coolant is used to keep the engine in a specific operating temperature.