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[robson]

My heater hoses go to a pump? mounted on the left side  of the engine bay looking from the front these hoses get hot even though I have no heating switched on is this right does this pump?  allow a flow all the time or should it only allow flow when heat is required in cabin.

[Lizzie_Zoom]

If I recall correctly the HBV controls the input of heat into the cabin when required.

The hoses will always become hot but the HBV stops the flow until 'told' otherwise.

[robson]

Thanks Lizzie is that a pump and what is its function I am looking for a reason  other than the stat for a low engine temp Trying to avoid the stat change.

[Kevin Wood]

I'm afraid, if it's running cool, it's probably the thermostat.

Heater flow is only blocked off when the climate is set to "LO" and air conditioning is active, IIRC.

[Marks DTM Calib]

And the pump is there to push hot water from the head through the heater matrix giving faster cabin heatup times.

[Andy B]

If I recall correctly the HBV controls the input of heat into the cabin when required.

The hoses will always become hot but the HBV stops the flow until 'told' otherwise.

You're at crossed purposes Lizzie. There's a pump on some cars under the header tank as well as the HBV ...... 2 separate things 

[Entwood]

If I recall correctly the HBV controls the input of heat into the cabin when required.

The hoses will always become hot but the HBV stops the flow until 'told' otherwise.

You're at crossed purposes Lizzie. There's a pump on some cars under the header tank as well as the HBV ...... 2 separate things 

But that pump only works when the engine is NOT running and you select heat to the cabin, its part of the "winter pack" and has nothing to do woth "normal" flow when the engine is running.

At least that is how I understand it, and how mine works !!!

[Andy B]

If I recall correctly the HBV controls the input of heat into the cabin when required.

The hoses will always become hot but the HBV stops the flow until 'told' otherwise.

You're at crossed purposes Lizzie. There's a pump on some cars under the header tank as well as the HBV ...... 2 separate things 

But that pump only works when the engine is NOT running and you select heat to the cabin, its part of the "winter pack" and has nothing to do woth "normal" flow when the engine is running.

At least that is how I understand it, and how mine works !!!

I don't have one on my car, but Mark, above, suggests otherwise ..... "And the pump is there to push hot water from the head through the heater matrix giving faster cabin heatup times." But I believe it also does as you say when parked up. 

[Lizzie_Zoom]

If I recall correctly the HBV controls the input of heat into the cabin when required.

The hoses will always become hot but the HBV stops the flow until 'told' otherwise.

You're at crossed purposes Lizzie. There's a pump on some cars under the header tank as well as the HBV ...... 2 separate things 

Ah!  Thanks Andy

Didn't know that.  With mine, as with so many older car designs, I always thought the main engine water pump supplies the pressure to the whole system. 

You never stop learning with miggies!

[symes]

If I recall correctly the HBV controls the input of heat into the cabin when required.

The hoses will always become hot but the HBV stops the flow until 'told' otherwise.

You're at crossed purposes Lizzie. There's a pump on some cars under the header tank as well as the HBV ...... 2 separate things 

Ah!  Thanks Andy

Didn't know that.  With mine, as with so many older car designs, I always thought the main engine water pump supplies the pressure to the whole system. 

You never stop learning with miggies!

Especialy v6 ones 

[robson]

I am still confused.What is the pump in the heater hoses for and when should it be running

[Kevin Wood]

I am still confused.What is the pump in the heater hoses for and when should it be running

It's there to circulate coolant through the heater matrix. This is normally done by the main engine water pump. The additional pump allows the climate control to use heat stored in the engine to keep the car warm while the car is temporarily parked. It may also run to boost the flow available from the engine coolant pump.*

* - I only ever provoked mine into running when the climate was turned on with the engine stopped although I guess it might run at other times to boost the flow available (e.g. when the engine is still warming up and the coolant is not up to full temperature or when outside temperature is extremely cold).

Incidentally, I removed mine during my LPG conversion and have noticed no reduction in heating. Might have been a different story if I lived in northern Canada, I guess.

[robson]

The pump must have a bypass so that there can be flow when the pump isnt  running perhaps the pump only boosts the flow when required. Does the heater matrix have heat all the time and we only realise that  when the fan switches on to transfer heat to the cabin.