My oil fired boiler is blocked and there is no water feed into the boiler and therefore no hot water or heat. I'm told there is scales or sediment that blocked the water feed pipes. I closed down my mainto repair a leaky circulator then turn it on and there is no water going in oil burner. How do I unclog the blockage. I was told you need to use a air compressor. Hook it to the cold water line for example on the washing machine cold water valve, open the hot water faucet in the bath tub and then turn on the compressor. Is this right, please help with any suggestions.

When you shut off the water supply for the repair, you may have dislodged some mineral build-up from the valve that has found its way into the strainer on the pressure reducing valve serving the boiler. If the valve you closed serves only the heating system, and it is a gate-style valve, the stem may have stripped or broken away from the gate.

I have never heard such crap. You will not block up a cast iron boiler with crud. If it worked before you changes the pump it should work OK. I think it may be the valve issue KC13 stated or air in the system. Air will keep the system from flowing.