My condensing boiler turns on and fires up as normal. It heats up the rads all through the house. After a while the boiler is still making a noise but the rads are stone cold. The only way to get the heating on again is to either wiggle the room thermostat which is up to max on the staircase or to continually turn the boiler on/off on/off. It thens works again and the whole process repeats itself.....Is it a boiler problem?