Combi Boilers - Hot Water Preheat function - Worth it?

b830ag2

Me again,

Got a couple of thread going on general boiler replacement issues...

Just wondered...in my research into Combi boilers (I think I will be converting my system from standard vented to Combi unvented), I have found that some offer a Hot Water 'preheat' function.

This, apparently, is to improve the time period between turning the tap on and receiving hot water, as apparently combi boilers are notorious for a long delay before receiving hot water at the tap.

1) is the general hot water combi delay true? is it excessive?
2) does a boiler preheat function improve this delay?
3) if so, is it worth the extra energy?

thanks,
Andy.

david29dpo

Good point. I have spent the last 6 months trying to decide which combi to buy and have come across these. I have come to the conclusion its something else to go wrong and wont bother.

rockin_plumber

I know the Worcestor Greenstar has an Eco button that allows you to turn off the pre-heat, so you can decide yourself if it is worth it then.
Great combi boiler as well!!

nobile

Yes - I say this after not getting a boiler with this feature 3 months back

Now we wait over a minute for warm water - used to be seconds

ormus

think it depends on your lifestyle. if the house is empty all day then its not really required.
ie if both adults work FT.
if the house is lived in all day then its a good idea. but even then we dont use the hot water much at all during the daytime.
we dont mind waiting the 15/30 seconds for the hot water to come through. its no big deal.

slipthru

Always had mine switched off, no problem waiting 20 seconds for water to heat up.

Moss5

If I use the hot tap 3-times a day and the shower/wash hand basin, say twice a day, I may be wasting 25 litres of drinking water/day. I am not on a water meter, but I have paid to soften that wasted water and feel a little guilty about it.

During the winter months, the combi boiler is providing central heating so the boiler is always warmed up.
Use of the hot water tap diverts all the heating effort to provide hot water, but any cold water in the pipe-line has to be driven out before hot water arrives at the tap.
During the summer, use of the hot tap is followed by a delay while the boiler fires-up.
A considerable amount of water is wasted before hot water reaches the tap.

A small volume of pre-heated water would reduce that delay and the waste.

Hotels (and large houses) use a system that continually circulates hot water through the pipes so that it is available without delay.

I have solved the problem with my 'old' combi boiler by introducing a small (15-litre insulated) electrically-heated tank in the hot water pipe-line. The tank is fed with hot water from the combi boiler, so the electric heater seldom comes on. During a long rest-period, it will maintain the temperature set on its own thermostat.

If I were buying a combi boiler today, I would opt for the type with a pre-heated storage tank.

roses

b830ag2 wrote: »

1) is the general hot water combi delay true? is it excessive?
2) does a boiler preheat function improve this delay?
3) if so, is it worth the extra energy?

thanks,
Andy.

Hi, I got a new boiler in February after my loft conversion. I replaced a 7 year old Potterton combi with a Worcester combi.

1) Not excessive at all. It takes about 15-20 seconds for hot water to come out the shower. For the space trade off of not having a hot water tank, it is worth while.

2) Mine has a pre heat function and does not save anything noticeable compared to the last boiler which didn't have it. Apparently it is only noticeable if you are drawing two hot water feeds ie someone having a shower & a hot feed washing machine.

3)My gas bill (I am comparing units used, not cost compared to same period 1 year ago) has increased by 20% since I installed the new boiler and this is due to the hot water store being kept at a fixed temperature. You can turn it off but it causes limescale build up and reduces the lifespan of the boiler.

I personally would have preferred a boiler without the hot water store to save ££ but the Worcester was the only boiler which would fit into the space I had & it had the highest rated hot water flow rate as I wanted a boiler that could cope with 2 showers simultaneously.

dander

I have recently gone from an old back boiler system with a hot water tank to a combi. I found with the old system I had to run the tap for a bit before the hot water made it to the tap anyway and my new boiler (no magic pre-heat) doesn't seem to take any longer than the old system.

To my mind there's a limited number of times you waste water with running off the tap anyway - if I wash up, have a bath or wash my face, I have the plug in straight away and I use that bit of extra water anyway. Washing my hands I most often soap up with that bit of water regardless of temperature and it's hot by the time I rinse. Bearing in mind that my metered water bill shows I used less than £50 worth of water in the last 6 months in total and I pay over £30 a month direct debit on gas costs, I think a little bit of water wastage is bound to be cheaper than an increase in gas use.

beetlebum_2

I personally think the water pre-heat function is great. I have it on my WB Greenstar and make use of it all the time. Comes in handy when having a shower or running the hot tap in the bathroom, as the pipe runs are quite long, and I hate wasting water. Being the frugal person I am, I press the eco button before I have a shower and get nice hot water really quick. I find that if I don't, a) it seems to take ages and b) it warms up gradually and takes quite a while to get piping hot.

molehole

beetlebum wrote: »

I personally think the water pre-heat function is great. I have it on my WB Greenstar and make use of it all the time. Comes in handy when having a shower or running the hot tap in the bathroom, as the pipe runs are quite long, and I hate wasting water. Being the frugal person I am, I press the eco button before I have a shower and get nice hot water really quick. I find that if I don't, a) it seems to take ages and b) it warms up gradually and takes quite a while to get piping hot.

Pre heat is Expensive and wastes a lot of gas, that is why Jersey Gas disconnects every pre heat on all combi boilers on the Island.
If your combi only fires for 30 seconds every hour (which is very conservative and can be a lot more especially if you have a dripping tap) it will cost you a minimum of £116.00 per year in gas (I can give the calculations if required).
I,ve installed the new Combisave device which is brilliant as it delivers near or better pre heat performance but without using any energy.