If central heating and hot water are both on - which wins?

[dominoman]

I have a boiler that has a central heating controller and a hot water controller.

There is a divertor valve that sends the boiler's water to either the central heating or into the hot water tank coil.

If I turn it on for an hour before work, with both central heating and hot water needing to be heated - which one will get precedence?

 

[45yearsagasman]

Neither will have preference. The water will heat quicker if you select HW to come on first. Do you have a fault?

 

[dominoman]

No. No fault. I was just wondering which one gets the hot water from the boiler if both are calling for it.

 

[JohnD]

both, if you have a hot water cylinder. It is possible to have a system that gives hot water (or heating) priority, but this is not usually necessary now. If you have an insulated cylinder it will still be hot from the previous night.

In a typical house, the cylinder can absorb less heat, so it will warm up faster from cold without the radiators.

However most modern modulating boilers have more than enough power to heat both the cylinder and all the radiators, and will adjust the flame size to suit demand.

I did once have an old, underpowered boiler, and if you had a bath on a frosty night, you could feel the house cool down as the radiator temperature dropped. My modern boiler has twice the power and hardly ever needs to run at full power for more than a few minutes when starting up from fully cold.

However, if you have a combi boiler, it will stop heating the radiators while you run hot water. Unless you are having frequent long showers, this will not be for long enough for the radiators to go cold.

 

[kbdiy]

Factors like resistance in the pipework would have some effect and would depend on the proximity of the boiler to the cylinder. Some installations incorporate some kind of flow restrictor in the hot water circuit to balance the flow rates and any bypass circuits could have some impact. All relatively minimal but possible I guess.

 

[dominoman]

In that case what is the 3 way divertor valve (AB) there for?

I thought that was used to send the hot water from the boiler either to the hot water tank or to the central heating pipes. Wouldn't it always need to send the hot water from the boiler one direction or another but not both?

Perhaps I misunderstood its function.

 

[jackthom]

It can also have both ports A and B open together when heating and hot water are calling for heat.

 

[dominoman]

It can also have both ports A and B open together when heating and hot water are calling for heat.

Ah. Didn't realise that. Thanks.

 

[twgas]

Just to add my six pennies worth, in the old days, a diverter valve would only have one port open and usually give hot water priority. The more usual valve used nowadays is a mid-position valve which can supply both heating and water.

 

[Agile]

Having said that, unless the HW circuit has a balancing valve then on most installation the HW takes most of the boiler's heat.

On a system with a correctly adjusted balancing valve, the CH and HW can run together with less impact on the heating.

Tony

 

[stardanny]

Op, what make is the diverter valve?

There is two different type, a diverter valve that only go to port A or port B and a mid-position valve that go to port A or port B or both at the same time.

Both heating and hot water coming on, diverter valve give priority to hot water first.

Daniel.