I read on here somewhere that 156s can have thermostat issues and last night on a run to Oxford noticed the heater did not seem as hot as usual - is this a sign of thermostat problem?

Have you checked that the coolant tank is full?

Air lock?

The stat on my V6 was stuck open.
The heater only got warm, not hot. The temp gauge didn't get to 70.
With a new stat, the heater gets hot and the gauge is at 85 on a run and the fan kicks in just over 90.

What does your gauge get to?

Also, have you changed the pollen filter since you've had it? It's under the scuttle panel on the passenger side. My 'properly serviced all its life' cars filter was choked and that was restricting air flow into the car.
I got half a bag of 'compost' off of the bulkhead at the same time

I might have posted this elsewhere, so apologies if I did.

Before going for a thermostat issue, plug an OBD connection in and check the engine temp as the car warms up. My 1.8 156 temp gauge seems really inaccurate as not reading much above 75, and I thought it might be a thermostat problem, but the signal the ECU is getting from the engine temp sensor is fine.

If that checks out, could be an airlock, stuck flap, servo motor, or if cable controlled, the cable might have slipped and the air mixing flap is not fully blocking the cold air supply. See if the heater temp goes up when recirc is on (no cold air coming into the car)

Thanks guys for your replies. The temp gauge sits at just under halfway between 50 and 90 on a run.

Hmmm.
Let it run at a fast idle til the rad cooling fan kicks in.
If the gauge is below 90 when it kicks in then it's under reading.
If it takes an age to get to 90 plus and the fan kick in then it's probably the stat.
If it warms up to 90 plus and fan kicking quite quickly then it's flaps - you know, heater not working properly.

Oh I'm so grateful to you guys - car was really low on water. So glad you suggested that, could have had a seized engine! Just hope there is not a leak, will have to keep an eye on it. Huge thanks. x

My 156 always seemed to run cool, and the heater took forever to get any heat.

A new thermostat sorted that.

How's the water situation, Annie?
Have you used much this week?