Hi, Heater has started to blow only warm air, not hot. previously it was like a furnace. I’ve never had to turn the knob past 22 even in the deepest winter. Coming home tonight and the heater was only warm.
Any tips or advice on what to look for, or what I should try first?
Thanks guys 
How is the temp gauge? Low and fluctuating? Could be a stuck open thermostat.
Hi, that was quick 
Temp gauge is steady in the normal temp position.
If it has Climate Control it aims for a temperature until it reaches that temp (heat up, or cool down if A/C allowed). Then it throttles back so as not to over-egg the pudding. It might be thinking you have already reached the warm temperature when the outside air is 25-ish.
Try it on fully clockwise past 29, it might surprise you. Or even try the boost for demisting the windscreen.
Hi, I was hoping that’s what it was, but the outside temp had dropped to around 15 degrees and even with heater set to max heat it was only warm air, not hot coming out. 
My gauge used to sit in the normal position but took an age to get there. Then when I wanted heat into the cabin it would drop slightly, the heat was only warm and took an age for it to heat up to how I wanted it if it ever did.
New stat sorted it. I don’t know if climate controlled fitted cars differ re the stat operations, shouldn’t do I’m thinking, they all take heat from the engine and circulate it.
It might be worth checking your coolant level.
Coolant level OK, bang on the F line.
Worth considering loose heater control linkage, blocked matrix, air lock, all unlikely in my opinion and more chance of it being a thermostat stuck open or perished if all is else is ok, but I am no expert!
I guess what you can try first…
Get the engine up to operating temp take a note of position the gauge sits at, then switch on the cabin heater full (no climate on) take note if the gauge moves, give it a few minutes. Mine dropped a couple marks, it was definately a faulty stat. Now it sits as before rock solid in the same position whether heat on or not.
I’ve been wondering about my thermostat recently. Took the photo after a good 20 minute fastish drive then reversed into the garage so probably a minute or so with no airflow. When moving the temp gauge is at least two notches cooler. Heater blows warn but temp up to its usual place within 2 -3 miles, 5 mins max. 
It sounds ok but try my suggestion above.
My stat failed in winter so more noticeably when wanting heat but very little of it emmiting out of the vents for clearing a very made up screen.
Usually it gets like a furnace blowing at you even in winter, so good are the heaters on a top down winters day. If that changes apart from checking the vitals like coolant level or for leaks take a look at the gauge and make a note of where it sits, heater on heater off.
Some say it’s about as good as it gets as a gauge.
Thanks Mick. Don’t mind doing it but I’d prefer to leave it be if it doesn’t need doing
What I did mean is try just putting the heater on full and see if the gauge drops, give it a few minutes.
Someone will correct me if I’m wrong but having a faulty or failing stat can make the engine run at the incorrect temperate thus affecting such things as fuel economy.
Usually when this happens it’s a failing thermostat. Mine did exactly this. The temp gauge got up to it’s usual place just about but the engine was running a full 15 degrees [C] cooler than it should. The temp gauge in the mark 3 [as with oil pressure “gauge”] cannot be relied upon to do anything useful, I now have a proper separate temp gauge which shows that the standard temp gauge responds way too early and shows fully warm before the car is anywhere near it. The same happens when the car gets hot too, the standard gauge sits happily at the normal mark whilst the engine is actually nudging 100 degrees. By the time the standard gauge has recorded any significant rise in temp you’ve already cooked the motor.
A simple OBD2 reader attached to your phone will tell you what temp the engine is really running at.
I’ve got one of those infra red thermometers - what temps can I expect where with that.
not got one of the OBD2 bluetooth things - anyone recommend one?
Engine should run at about 82-85c. Use the heater hose that goes into the heater box for your infra red thingy. Note that while stationery your engine will get hotter than if your are moving so take temp after a drive before it gets a chance to heat soak
Bought one of those obd 2 dongles. Took the car for a short drive. 5 miles. Temp steadied at 69degrees. Raising to about 74 waiting at junctions and 86 after 5 mins of idling on the drive after the run. Verdict on the ‘stat?
Change the stat.
What he said 
