MG-Rover Technical and Information Pages

Replacing cabin heater matrix valve on the 2004 ZR

The only really serious problem that Ive had with the cooling system since getting the one owner ZR in 2010 was with the experience of having no heat in the cabin. I had replaced the radiator, which was very badly corroded along the bottom edge, most probably due to a long term weak and incorrect coolant mix, new top and bottom radiator hoses were also fitted at the same time, also adding a correct fill of fresh coolant.

Using a further trial and elimination process, the cabin heater control dial was set to hot position, radiator bottom hose detached and coolant drained off yet again. For this purpose a clean and cut to shape washing up bowl was used. The first to check were heater control valve located on the bulkhead, the cabin heater control dial, and then the heater matrix. 

heater control valve

Cabin heater control valve JJB-100240

Although removed at this stage, for cleaning and the slider valve greased, it shows matrix heater coolant pipe, and cabin heater dial control rod just evident at the side. 

Cabin heater controlled coolant valve location shown above is at the rear of the engine and attached to the bulkhead, and is nothing more than just a simple sliding coolant regulator or shut off valve, that is operated directly when rotating the cabin's heater dial for either hot or cold air, this had no issues with opening or closing, and was working as it should. Checking the heater control dial for freedom of movement, this was rotated a number of times from hot to cold position, confirming that the sheafed steel operating control rod was working correctly and had not become detached and functioned in an un-restricted and smooth operation.  


heater matrix valve

Cabin heater matrix valve PCH-003300

The heater matrix valve as shown, is basiclly a SAAB C900 unit and usually comes supplied with 4 new coolant hoses already attached. 

Next to check was a possibility of a blocked heater matrix, with a clean tube attached to the inlet pipe, a light blow through test expelled clean and clear coolant just same doing the outlet pipe, no blockage was evident. On further investigation, the heater matrix valve was now being suspected. The heater matrix valve, routes hot coolant which is circulating within the engine, to the cabin heater, an internal fault in the valve would restrict this process, so fitting a new one was now a good and much better option, especially on a vehicle of this age.

With a new valve fitted, and all coolant hoses attached, the cooling system could now be filled after first replacing the small loss of coolant from the cabin's heater matrix during my earlier test, the return hose, smaller of the two hoses attached to the elbow joint is located front of engine

Cabin heater return hose to matrix radiator 

Coolant loss was poured directly back into the cabin's heater to basically the same amount of coolant previous taken out  and so avoiding a possible air lock when filling the system. No specific amount, it just needed to be in there first. 

mg rover coolant elbow joint

With heater return hose attached, and heater dial still set to the 'hot' position, and with a 50/50 coolant and water mix, commenced on a slow filling procedure. A really slow fill is the key to a good result. When free flowing coolant does start to emerge for several seconds from the coolant rail, the 8mm bleed screw bolt can then be refitted back, this needed to be done 'without a break' from pouring in the coolant up to a maximum plus, fill level, before screwing back on the coolant cap, and then running the engine on tickover for several minutes.

Increased engine revs and radiator hose squeezing isnt necessary during this, the added volume of coolant should search out all areas within the system, coolant level when being checked on a 'cold engine' may need a tad to be syphoned out, my preference has been to retain at a constant maximum plus fill level without any problems. A fully working heater all year round, and especially during the winter months is essential.   

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