2 different plumbers have repaired it over the last two weeks and they both said that it could need to be flushed out. but neither of them provided that service so the quote is from a third company.
the heating takes aprox 2 hours to start working properly after the timer has started and if i put it on constant it doesn't always start at all and the house is frezing cold. we don't have a room thermostat.
the plumber said it could be an air lock and/or sludge in the system, but we bleed the radiators like every month cause there in always something wrong with them...
When the rads eventually come on, if they hot at the top and cold at the bottom, then they are sludged up inside. The simplest way of cleaning them, is to take each radiator off the wall and flush thru with a hosepipe. Remember to drain the system first. Also be careful not to drop any of the nasty black sludge on your carpets.
If the rads are hot at the bottom and cold at the top, the problem is air in the rads.
If neither of these apply, the problem is with the pump or the boiler. To check the pump, if it is external to the boiler, hold the pipes gently about ten inches either side of the pump. If both get equally hot within a couple of minutes, the pump is working. You will also feel a slight vibration.