I have an issue with no heat in my van.
- 1984 Hiace YH51
- 3Y motor
- Don't have any overheating issues and gauge sits where it always has for the past 20 plus years.
- Have replaced the heater control tap and verified that it is open
- Have replaced the thermostat and all hoses recently
- New radiator 12 months ago as the last one sprung a leak.
- System has been flushed a couple of times and is clean
- Heater core has been flushed separately in both directions and seems to have good flow
- Have removed the heater hoses from the core and started the engine but nothing pumps through the hoses.
- If I connect a hose to the disconnected heater hoses I can push water through the system in both directions which suggests that it is not a blockage and that the thermostat is open
- Have idled the motor at length to get it hot and increased revs without any obvious hose collapse

My initial thoughts were that I had a blocked core and not wanting to pull half of the car apart to fix it I flushed it out but no cigar. I haven't had any overheating issues so assume that the water pump is working correctly, just don;t get any flow through the heater hoses.

What circulates water through the heater hoses? Is it the general flow of water through the system? If so then why does water not flow when it flows freely with hoses disconnected and connected to a garden hose? Does the water pump perhaps have a separate function for circulating water through the heater and this part is defective even though the general circulation seems to be ok?

Would appreciate any thoughts as it is a bit chilly driving to work in the morning and having to use cold air for demisting the windscreen.

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