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[Ewan]

Can anyone please identify the round plastic, what looks like vacuum valve at the back of the engine. It has heater water pipes attached and has a sngle small bore vacuum pipe coming out of the top. I suspect it is leaking internally as steam and water came out of the pipe when I disconnected it. I don't know what it does and don't fancy trying to replace it, as I have only recently taken the inlet manifold off to give the pipes a clean. What would happen if I just blocked off the vacuum pipe? Sounds lazy I know but I'm getting a bit old for this sort of stuff.

[albitz]

Its the heater bypass valve.Its a common fault for them to leak.Dont think you will be able to blank it off or bypass it.About £40 iirc,not that difficult to change,just a bit awkward.

[Lizzie_Zoom]

It is the HBV (Heater bypass valve), and is relatively easy, but awward to replace.

Costs around £35 with TC, and if you remove the wipers and scuttle, folding back, then you will be able to get to this device and replace.  As I said previously, just awkward, but not difficult 8-) 8-) 8-)

Vx part no. 090566947

[feeutfo]

yeah, what they said....

[Ewan]

Many thanks for your replies. I think I prefer difficult to awkward. But what does the HBV actually do? I thought modern heaters had hot water running through at all times,and it was the airflow that was diverted instead, when cool air was required. Is it to do with the aircon?
Ewan

[Abiton]

Must be, 'cos non-aircon cars like ours lack an HBV.
Something of a blessing as the things seem absolutely reliably unreliable. 

[Andy H]

The Omega does use airside control (flaps) as the primary means of controlling the temperature but the HBV shuts off the water flow to the heater matrix when no heat is required to avoid cooking the dashboard.

It is arranged as a bypass to maintain circulation of coolant around the engine.

[Ewan]

Something doesn't add up here. Because I live in Scotland, and seldom need aircon, and with winter looming, I have just blanked off the vacuum pipe. But the car behaves OK, heat comes through when requested, as does cold cold air. All the heating controls seem to be working.

[Andy H]

I don't know if the valve is normally closed (and opened by the vacuum connection) or normally open.

Your evidence points to it being normally open (or else yours stuck open when it failed).

[RobG]

I would have thought if the HBV was stuck open/shut you would only get hot or cold through the system and not both :-/

[Boatboy]

Without vacuum the heater matrix is in circuit. By adjusting the temperature controls you get hot or cool air as required as per most 'normal cars'. I believe this is achieved by changing the proportion of air taken via the heater matrix. Even on cold air settings the heater matrix is still at engine temperature (hence the 'cooking the dashboard' comment), again as per normal cars.

Apply vacuum  to the hbv(controlled via a solenoid behind the glovebox, switched by the climate control or turning both temperature dials fully anticlockwise to operate 2 microswitch's) and the water is diverted back into the engine and bypasses the matrix, which will then cool.

I think the main purpose of the hbv is to keep as much heat out of the car, particularly when the aircon is on.

All that being said, steam or whatever coming out the vacuum connection of the hbv is wrong and sounds like a breakdown waiting to happen, and as the nature of these things is to happen when least convenient it might be best to get it sorted.

I believe others on here have done away with the hbv and plumbed the matrix permanently in line.


Steve

[Lizzie_Zoom]

Without vacuum the heater matrix is in circuit. By adjusting the temperature controls you get hot or cool air as required as per most 'normal cars'. I believe this is achieved by changing the proportion of air taken via the heater matrix. Even on cold air settings the heater matrix is still at engine temperature (hence the 'cooking the dashboard' comment), again as per normal cars.

Apply vacuum  to the hbv(controlled via a solenoid behind the glovebox, switched by the climate control or turning both temperature dials fully anticlockwise to operate 2 microswitch's) and the water is diverted back into the engine and bypasses the matrix, which will then cool.

I think the main purpose of the hbv is to keep as much heat out of the car, particularly when the aircon is on.

All that being said, steam or whatever coming out the vacuum connection of the hbv is wrong and sounds like a breakdown waiting to happen, and as the nature of these things is to happen when least convenient it might be best to get it sorted.

I believe others on here have done away with the hbv and plumbed the matrix permanently in line.


Steve

But what is the point when only £35 is involved, providing you can do this easy job yourself.  Is not that worth a fully working luxury car? :-/

[Boatboy]

Without vacuum the heater matrix is in circuit. By adjusting the temperature controls you get hot or cool air as required as per most 'normal cars'. I believe this is achieved by changing the proportion of air taken via the heater matrix. Even on cold air settings the heater matrix is still at engine temperature (hence the 'cooking the dashboard' comment), again as per normal cars.

Apply vacuum  to the hbv(controlled via a solenoid behind the glovebox, switched by the climate control or turning both temperature dials fully anticlockwise to operate 2 microswitch's) and the water is diverted back into the engine and bypasses the matrix, which will then cool.

I think the main purpose of the hbv is to keep as much heat out of the car, particularly when the aircon is on.

All that being said, steam or whatever coming out the vacuum connection of the hbv is wrong and sounds like a breakdown waiting to happen, and as the nature of these things is to happen when least convenient it might be best to get it sorted.

I believe others on here have done away with the hbv and plumbed the matrix permanently in line.


Steve

But what is the point when only £35 is involved, providing you can do this easy job yourself.  Is not that worth a fully working luxury car? :-/

I agree. Just offered the info to complete the picture. I just replaced the solenoid on mine, luckily I got one cheap from carpartsconnexion;)

Steve