Why do combi boilers have the need for a twin programmer?

[Inverness]

Can some clearly explain why a combi boiler would need a twin programmer when the hot water will always be priority over the heating.

I know that you could preheat the water so there is less time you wait for hot water to pour out of the tap. But surely that's what you expect from most combi boilers?

would there be a diffrence from oil combi to a gas combi apart from a gas modulates.

can someone give me answers please.

 

[Inverness]

Preheat oil combi button

Hi my sister has moved to a new house. Less than 4 year old. I noticed there is a room stat in the same room as a trv. (Conflicting with each other) bad practice. Any way They have a oil grants vortex Eco pro 26e combi.
As a apprentice We never install oil combi boilers. So I'm having problems understanding the preheat function. and when is the best times for this to be set to come on?

ive done a bit of homework and what I've found is a lot of people say the preheat function is a waste of money and energy.

Any advise I'd be happy to hear from you all.

 

[SimonG]

Oil combis have large heat stores that need to be up to temperature to provide water at specified volumes. If nobody is in all day then no point keeping it hot, likewise overnight. Ive seen the ho****er permanently on, on some older external combis. Prob did it that way so not to have to fit a frost and pipe stat.

 

[Inverness]

what times would you recommend for the preheat hot water to come on? will it take much longer for hot water to flow from taps if the water wasn't preheated because its a oil boiler? what would happen if you didn't use the preheat function and just demanded hot water when you opened a tap?

 

[SimonG]

Its not a preheat. Its a requirement for hot water. If the tanks cold then you will get cold water. The tank has to be hot as its that water that goes through the plate heat exchanger to produce the hot water. I normally programme it to come on half an hour before required and half an hour before the heating. But all depends on occupation and usage.

 

[Millsy 82]

Re: Preheat oil combi button

The preheat keeps the store up to temperature so when you turn the tap on you get hot water. I say to people either leave it on constantly or have it on from about 30mins before you get up until your bedtime.

 

[lame plumber]

Re: Preheat oil combi button

as above, or all youll get is cold water from the tank

 

[Inverness]

Re: Preheat oil combi button

I don't understand why you would only get cold water.

 

[Best]

Re: Preheat oil combi button

I don't understand why you would only get cold water.

The "store" will be cold water if the boiler isn't given power until you use your taps.
Think of it much like a copper cylinder needing to be heated from cold well before you need to use hot water.
The store is there for a purpose so it allows the boiler to catch up with replenishing the hot water when a lot of it is being drawn off.

 

[Inverness]

Re: Preheat oil combi button

Thanks very much and your time. So its not like a combination boiler without a storage facility by turning the tap on and a few seconds later hot water arrives. If i dont call to preheat the thermal store that's inside the oil combi and turn the hot tap it will run cold because the hot water plate exchanger isn't getting any heat transfer from the preheat storage facility?; meaning you can't have hot water unless the preheat function is on?

If you have small pipe runs and not the need for two hot showers in use do you still need the preheat?