The 1500 heater system uses an integral-blower heater case similar in principle to the later 1275cc system, adapted to suit the Triumph engine's revised engine bay layout. The heater matrix is the same unit as the later 1275cc system, but the heater case, mounting brackets, air intake hose, blower motor, and water connections are all 1500-specific. The control cable is 23 inches, shorter than either 1275cc cable length, reflecting the different dashboard-to-heater-box distance on the rubber-bumper car.
1500 Water Supply Arrangement
The critical difference on the 1500 is the water supply arrangement. Rather than using a heater tap mounted directly on the cylinder head (as on all 1275cc systems), the 1500 uses a separate water control tap and elbow assembly mounted on a bracket in the driver's footwell area. The water supply is taken from the thermostat housing via an adaptor and fibre washer, through hoses to the inlet manifold and then to the tap and elbow assembly, and onward to the heater matrix inlet. The return from the heater matrix outlet runs back to the inlet manifold area.
The hose routing on the 1500 is more complex than the 1275cc arrangement and can be confusing during reassembly, careful labelling or photography of the original routing before removal is strongly recommended.
Heater Tap and Elbow Assembly
The tap and elbow assembly is the Achilles heel of the 1500 heater system. The tap is prone to seizure due to limescale build-up and corrosion, and when it seizes, it typically seizes in the closed position, leaving the occupants without heat. The assembly can also develop leaks at the elbow joint and tap body, dripping coolant into the driver's footwell, often not noticed until the carpet is saturated and the coolant level has dropped. A heater valve kit is available that replaces the original tap with improved components offering more reliable operation and a more positive seal.
The gaskets between the tap, elbow, and mounting bracket should be renewed whenever the assembly is disturbed.
Heater Matrix and Blower
The heater matrix is shared with the later 1275cc system and can be renewed without removing the entire heater case from the car. The blower motor and fan assembly is a replaceable unit within the heater case. The heater box seal between the case and the battery platform should be renewed whenever the heater case is removed, as a perished seal allows cold engine bay air to bypass the matrix and enter the cabin, significantly reducing the already modest heat output of the system.