The Triumph 2000/2500/2.5 Register Forum

I went for a ride yesterday and found the heater not warming up (winter in NZ) - MK2 2000TC. What could be causing that? Would appreciate your input.

Assuming that the engine is getting up to normal operating temperature, the first thing I would try is a flush/backflush of the heater matrix. Disconnect the two heater hoses at the bulkhead and attach a garden hose to one of the two stubs of the heater matrix. After a minute or so connect the hose to the other stub and flush it the other way. You'll be suprised at the amount of cr*p that comes out! Repeat a few times in either direction until the water runs clear.
Try that and let us know how you get on

I would hazard a guess that possibly the solid cable from the heater control for the interior temperature that goes to the water valve on the offside (drivers side in the UK), has come way from its mounting clamp as a result of the water valve seizing. It's probably seized in the 'cold' position therefore not allowing coolant to circulate through the heater matrix. Bit of a fiddle to get to, but doable without removing too much trim - removing the drivers parcel shelf make access better. If you can free it off / get the valve out, a touch of Vaseline or rubber grease on reassembly will help prevent it sticking again.
If the heater control knob feels 'slacker' than normal, then this is a good indication that the valve has seized and the cable has pulled away.
N.B. This is assuming it is a MK2.....the MK1 is a lot easier to access from the engine bay, but isn't as prone to seizing like the MK2.