Heater blows cold only?

Hi, Paul,
A cold breeze round your feet isn't good at this time of year, is it? Couple of things it could be. Could be an air lock in the cooling system. When the engine's up to temperature, take off the expansion bottle cap....be careful as there may be boiling water spurt out. The air in the system will always find its way to the highest point in the pipework. Often, this is the expansion chamber or bottle. If that doesn't work, you'll have to try loosening the highest hose on the system and let hot water flow out for a second or two, as this release any air with it. The refix the hose and tighten the clip. Be careful as before...the water will be hot. You need to do this when the pressure's built up in the system to force the water and air out. If this fails, then the heater matrix may be blocked. Find where the hose goes into the heater from the engine...possibly at the back of the compartment or through the bulkhead, slcaken this off...do it when the engine's cold...then slcaken off the return hose....they should be close together...feed water into the heater unit through the pipes that the hoses connected onto so as to flush the heater matrix. A garden hose should do the job. Don't use too much pressure. Any sludge in the system should be flushed out. Only other thing it could be...not likely...is the heater control on the dash has become disconnected from the heater unit itself and isn't opening/closing the flaps on the heater itself. I would opt for an air lock in the system. Often happens when you've drained it then refilled it to put antifreeze in. Have a go...it sounds difficult but it's straightforward. Watch the hot water though from the engine. At normal temperature, it's not far off boiling.
Good luck!! Denis

Denis Langley (ex-mobile mechanic)
December 2006