Just moved into a house which has a boiler and hot water cylinder. Modern well insulated cylinder, oil fired boiler.

Last time I had a cylinder was about 20 years ago and hot water used to come on am and pm for a couple of hours but I recall reading somewhere (STW?) that it was just as efficient to leave the HW on permanently and let it maintain the temp of the water in the cylinder rather than having to warm it from cold/cool/lukewarm twice a day.

Any thoughts?

Leave it on timed. Energy loss is proportional to the temperature difference between the tank and the surroundings, so when you’re not using it you want that as low as possible.

We leave hot water on timed, unless someone is having a big bath. We do in winter leave the heating on 24/7 and water – our gas bill (including hob) is less than £45 a month. Do not ask about the electric, it’s horrendous (hot tub and two gaming PC’s).

When I moved into this house it had the HW cylinder always on with the boiler. I added a switched valve, separate timer and a thermostat on the cylinder itself.

We run it timed, twice a day for a couple of hours is enough but there are just the two of us so usage is pretty predictable.

Ours runs twice a day, 6 am for an hour and then 9am for an hour. Hot water for morning showers then a reheat afterwards to last the rest of the day in case anyone has a shower later on etc.

Going back many years to my days as a customer service bot for what was then British Gas the standard advice was that it would nearly always be more efficient, assuming the tank was well insulated, to have it on a timer but that it was worth experimenting for a couple of weeks leaving it on 24/7 to see for sure as every house/installation is a bit different.

So, take a meter reading today and another in a couple of weeks. The switch to 24/7 and take another reading in another couple of weeks.

Two weeks was deemed acceptable because it is long enough to see a difference but not so long that it will make more than 50p-£1 difference in the monthly bill.

Repeat if you feel necessary in winter.

Although that’s only going to work if the heating is switched off – and even then it’s flakey as it doesn’t take into account changing useage.

Timer for me – nothing more annoying that hearing the boiler fire up (at the end of a shower) to heat water that you know isn’t going to be used for 24hrs.

timed.

match it up to your regular use pattern.

e.g. for us that’s mainly evening baths for the kids, so it comes on late afternoon for an hour or so

Timer for an hour 5pm

210 litre tank does the 4 of us shower in eve.

Modern tank but also insulate the hell out of it, old duvet wrapped around etc.

Also have solar PV diverted to immersion heater during the day so boiler hardly has to come on anyway.

When we moved in it was set on all the time, annoying hearing it kick in periodically at night for water the next evening…

Wowsers – a whole thread of agreement. Thanks folks, now set on timer 🙂

Both CH & HW are on the same timer, winter sees both running, summer is HW only – set to come on about 90mins before we get up to take the chill off things in winter, turns off shortly after we get up. Then in the evening, set to come on about 90mins before we get home but then stays on until about 8pm, when it starts getting a bit nippy – we go to bed!

Timed here – 6-8 in the morning, 5-10 in the evening

I do 1 hour late afternoon and there always seems to be enough hot water for washing up showers and baths for the children. on mine there is a button so you you can put it on for an extra hour if I need extra hot water but don’t tend to do it that often.

I can set it up for two or three times a day but I imagine it would only be on for a very short time for those each of those intervals as it holds the temperature really well.

we have ours on timed then use alexa to boost it if needed (in the morning when guests are staying or one of us wants a late bath or something).

I’d ideally like it if there was something that could be set to boost the temperature in the tank to 60C once a week at midnight to kill off the legionarres and let things cool down so we don’t get scalding water through the taps, but it doesn’t seem to exist

we have ours on timed then use alexa to boost it if needed (in the morning when guests are staying or one of us wants a late bath or something).

I’d ideally like it if there was something that could be set to boost the temperature in the tank to 60C once a week at midnight to kill off the legionarres and let things cool down so we don’t get scalding water through the taps, but it doesn’t seem to exist

You could manually turn the stat up on the tank for an hour and back down again whent he boiler is running if Alexa doesn’t know how to do it.

As an aside what temp do people have their hot water set to?

My solar fuelled immersion is turned right up, the oil fuelled stat at 50 degrees.

My solar fuelled immersion is turned right up, the oil fuelled stat at 50 degrees.

Interestingly mine’s the same – I can always tell.if the water was heated by the solar as it’s maxed.out at 61c while the boiler thermostat was set lower.