My blowers are usually very efficient when it comes to roasting me to death ... even when on 18 degrees i find myself driving around with the window open... in the recent weather they have been much appreciated... today though they have struggled to get above what i would call 'a bit warm' ... i drove for about 25mins with the controller sat on 30 degrees with no improvement in their output. I had a new heater matrix last year so im ruling that out.. temp gauge is fine .. so im thinking maybe its something to do with the dial that sets the temp - anyone had an issue like this?

I take it you’ve checked the first thing I would always check with regards to my heater giving out less warm air or even cold on hot setting

The coolant level

I checked the coolant and the level is bang on midway between min and max

It could be

1. coolant level and also
2. thermostat stuck open
(but you say temp gauge is OK, so unlikely to be those)
3. temperature control knob resistor contacts dirty/broken - you can check the resistances with a multimeter when you move the knob
4. (some other electrical connection problem)
5. the interior temp sensor/fan is not working (between the A/C and recirc buttons) - a fairly common failure
6. the temperature control flap that sits above the heater matrix could be stuck in the "up" position so that no air is being directed through the matrix, and it all bypasses.
7. A/C and heating ECU (next to blower motor) could be faulty. Swap with a known good one if you can.

I had a problem with this flap being stuck in the "down" position so that all the air went through the matrix and I was roasting. I replaced the actuator motor that moves the flap, but it's difficult to get to.

With ignition on (but engine not running) if you turn the temp control to max heat and then max cold and back again, you should be able to hear (if you listen carefully) the actuator motor running to move the air control flap. If you hear nothing, the flap could be stuck (or not moving because the control knob/connection is faulty)

Thanks Dave.. lots of things to check there ... interestingly they were back to drying out my eyeballs this morning ... i think option 6 sounds most likely actually perhaps its sticking in the on and off position making it either hot or cold and nothing in between