Combi boiler pre heat

[Matt0029]

On average how much a year would you suggest it cost to keep.the hot water preheat on. On a combi boiler. Thanks.

 

[ShaunCorbs]

It’s one of them boiler doesn’t have to work as hard on start up and you don’t waste too much water waiting so I would say around even

 

[Matt0029]

So leaving it on isn't really a bad idea?

 

[Scott_D]

Would be good if you could time it to be on during times hot water will be used and off at night or at work.

 

[Matt0029]

Would be good if you could time it to be on during times hot water will be used and off at night or at work.

I think some do offer intelligent pre heat so it remembers when you use hot taps and pre heats at a similar time to following days.

 

[IND_Nick]

With the Worcester combination boilers you can set pre heat times like a hot water setting, obviously if the stat is compatible. Work's well with the Nest etc. Just need to wire in the HW like a system programmer.
I'm sure there's similar on other manufacturers.
In general I doubt it uses much in the way of gas consumption and £'s as mention above it saves when you do need it to fire up and water costs. Also for 5 months of the year when heating is on it generally wouldn't be utilised much as boiler already up to temp when you need hot water.

 

[Matt0029]

Any idea why I think it's mainly the boilers with allumunim hexs that offer pre heat?

 

[John.g]

If preheat is available on a non storage combi is there much difference in hot water availability than without preheat?.

 

[EvilDrPorkChop]

If preheat is available on a non storage combi is there much difference in hot water availability than without preheat?.

Yeah it does make a difference.

Unless it's a long run, I leave the feature switched off. More wear and tear on the boiler that's just not needed. Diverter moving every hour, fan and gas valves kicking in. To what? Save 10 secs of HW delivery. It'll use more gas £ than you waste in water £.

The comfort feature on the Vaillants does work really well, but like I say unless it's a long run it isn't needed IMO.

 

[Matt0029]

That was my slight concern if caused issues long term if left on.

 

[Matt0029]

That was my slight concern if caused issues long term if left on.

Can it possibly cause issues?

 

[EvilDrPorkChop]

Can it possibly cause issues?

I've seen diverters prematurely fail, and i'm sure it'd shorten a boilers life. But by how much, is unknown. It's such a variable factor.

 

[Matt0029]

I've seen diverters prematurely fail, and i'm sure it'd shorten a boilers life. But by how much, is unknown. It's such a variable factor.

Fit one for an oldish lady in a loft she requested the pre heat be left on. As complained the last boiler took too long for water to get hot. Awkward for here to ever turn the pre-heat off with where its located.

 

[EvilDrPorkChop]

Fit one for an oldish lady in a loft she requested the pre heat be left on. As complained the last boiler took too long for water to get hot. Awkward for here to ever turn the pre-heat off with where its located.

Sure it'll be fine. With the lengthy manufactures warranties these days as well it'll be covered for 5/7/10 years dependant on manufacturer.

 

[John.g]

If a PRV is fitted on the incoming mains, is there not a danger that the pressure will rise excessively high due to expansion as there is no HW flow during preheat?

 

[EvilDrPorkChop]

If a PRV is fitted on the incoming mains, is there not a danger that the pressure will rise excessively high due to expansion as there is no HW flow during preheat?

With the such small storage of water I imagine the expansion is very minimal. Never had any issues myself, but then again I rarely leave the feature on.

 

[IND_Nick]

Essentially the boiler is in the same state on preheat as it would be if you had just used the DHW and turned the tap off. It has heated primary water in it and just the plate to plate so very little volume, I've never heard of it causing issues.

 

[John.g]

What preheat temperature sensor is used with preheat?, if its the primary (boiler) water then maybe the diverter valve doesn't c/o during preheat.

 

[Matt0029]

Guessing there is only say 1 litre of water in the plate?

 

[Matt0029]

I was reading up on it and I heard on the old ideal isars, you couldn't even turn preheat off. You had to buy a preheat disable kit.

 

[Matt0029]

With the such small storage of water I imagine the expansion is very minimal. Never had any issues myself, but then again I rarely leave the feature on.

Similar to my situation never really leave it on. Just on this one installation.

 

[Matt0029]

Can anyone help elaborate on what is meant by the last 2 points please? Also if the temperature is measured on the flow thermistor the pre heat would come on more in the summer? As the primary flow of the boiler won't be at temperature as the heating wouldn't be getting used.

 

[ShaunCorbs]

Yes because the heating isn’t on keeping the boiler hot so would come on more in summer

 

[Matt0029]

So possibly somethings one could advise to maybe turn it of in the summer months?

 

[ShaunCorbs]

You will have a longer wait for hot water then ?