Hiace Weak Heating Error

I had a similar issue with my Hiace. Check for valve blockages or coolant leaks first. Could be the heater core too.

Where exactly should I be looking for these blockages? Is it easy to spot?

Hard to say, really. Check the valve and its connections carefully. If you aren't comfortable, I'd suggest a workshop. That's what I did, anyway.

Right, makes sense. I'll take it in. Turns out, faulty connection, as I suspected. New plug, all good. Cost me 95€. Thanks for the advice!