Weather compensation

[fixitflav]

A query that comes to mind.

What do you do if you’re installing outdoor temperature compensation with a conventional system – heat-only or system boiler with diverter valve and HW cylinder?

As the boiler flow temperature is reduced by the outdoor temperature compensation it could be too low to heat the HW cylinder, so having both CH and HW together, using a mid-position valve (Honeywell system Y) doesn’t work. (Unless more features are added e.g. allow mid-position operation when the boiler flow temperature setpoint (via the outdoor controller) is say 5° higher than likely maximum cylinder stat setting.)

On a new installation, am I right thinking you would use an either/or diverter valve, with HW preference?

In a case of retrofitting outdoor temperature compensation, if the system has a mid-position valve, how would it be handled?

As I believe mid-position diverter valves are nowadays much more common than either/or, and the latest regs require outdoor temperature (and even weather, via the internet) compensation, I would guess this situation has been considered.

Similar, but slightly different problem with two 2-port valves instead of a diverter.

 

[steadyon]

Personally I'd use an "S" plan. Because:

1. You need separate times for heating and hot water.
2. I find the two ports (generally use Honeywell) more reliable and longer lasting than three ports.
3. I find the wiring is simpler.

 

[ShaunCorbs]

Hw prioritie

 

[fixitflav]

Hw prioritie

That's what I thought. Maybe the old V4044 valve will make a comeback.

 

[fixitflav]

1. You need separate times for heating and hot water.

I suppose you mean separate on the valve(s). Separate times on the programmer would be OTT.

3. I find the wiring is simpler.

Compared with a mid-position valve, probably. Compared with either/or, not much to choose IMO, by the time you've wired up the auxiliary switches in the 2-ports. But each to his own!

 

[Gasmk1]

or you could just go with the 4 pipe boilers by vaillant or viessmann

 

[chris watkins]

Just Swop Mid position for a diverter.
Converted my existing S plan wiring so I could install a Viessmann heat only with WC a few years back just needed a Horstmann Channelplus programmer.

This is why BoilerPlus just applies to combi's but I think it should be all boilers!!
Discuss......