I have a two story home. The hot water from the boiler does not reach the radiators on the second floor.Several attempts to bleed the system upstairs did not solve the problem. At the boiler, the water temperature reads close to 180 deg. F. the pressure reads 0. The pump is running and the air in the expansion tank is bled also. ANY SUGGESTIONS?

Yes you water pressure is way to low. Try about 12 pounds for starters. If you have a auto fill valve it might be defective.

Thanks for your reply. I looked at the automatic water feeder, it's integrated in the expansion tank. Does that means the entire unit should be replaced?

If it is threaded on the different fittings then the parts can be replaced separate. Now in some cases due to age it might be better to replace the entire assembly especially if it had a bladder type tank.

Remember you only replace things that are proven defective. The auto water fill valve might need to be adjusted etc. Also make sure the water line that feeds the valve is open. I have seen where the water line valve is turned off and the boiler would get no water so check before replacing.