Hi all, my focus heater has just stopped producing hot or cold air. The blowers work fine, all the lights on the climate control come on but the temperature never changes. Also recently it overheated and I spotted that the coolant reservoir was nearly empty. I check it every few months. So it's drained since I checked it last. Refilled the reservoir wondering where that coolant is now as there are no puddles in any of the foot wells, wet patches in the engine bay or brown gunk in the oil. I've read that these might be connected around the heater matrix but getting to that is a massive job so I'm finger crossing that it's going to be an easier fix.

Any ideas?

The heater matrix will be full of air rather than coolant now, so that explains the lack of heat.

The air con gas has probably all leaked out, which would explain the lack of cold.

But the loss of coolant is by far the biggest issue here.  That's one of the most common reasons for engine failure.

If you can't see it in the footwells and you can't see a puddle underneath them it's unlikely to be leaking from the matrix.

Check the reservoir for any cracks.  Check the lid spring still moves.  Or just replace both if unsure.

Then bleed the system thoroughly, that should restore the cabin heat and prevent any further engine damage.

On 6/22/2025 at 6:00 PM, TomsFocus said:

The heater matrix will be full of air rather than coolant now, so that explains the lack of heat.

The air con gas has probably all leaked out, which would explain the lack of cold.

But the loss of coolant is by far the biggest issue here.  That's one of the most common reasons for engine failure.

If you can't see it in the footwells and you can't see a puddle underneath them it's unlikely to be leaking from the matrix.

Check the reservoir for any cracks.  Check the lid spring still moves.  Or just replace both if unsure.

Then bleed the system thoroughly, that should restore the cabin heat and prevent any further engine damage.

Still, where is it going? No puddles in or outside anywhere, no sweet smell, nothing.

Replace the plastic expansion tank and also fit a new filler cap.

10 hours ago, Jazzmag said:

Still, where is it going? No puddles in or outside anywhere, no sweet smell, nothing.

Evaporating into the atmosphere past a weak cap or split in the reservoir most likely.

If not then it's burning inside the engine, which would be a much more expensive repair.

3 hours ago, TomsFocus said:

Evaporating into the atmosphere past a weak cap or split in the reservoir most likely.

If not then it's burning inside the engine, which would be a much more expensive repair.

It's not in the oil thankfully.

7 minutes ago, Jazzmag said:

It's not in the oil thankfully.

That does not prove the headgasket hasn't failed.  Oil & coolant mixing isn't particularly common with headgasket failure in my experience.  Generally the only symptoms are coolant loss and overheating.