My mother had one, pain in the neck, with storage turned on, if one goes for a shower it starts cold, gets warm, then goes cold and finally gets warm again, so wastes gas running the shower until it stays warm before going under it.
Turn the storage off, and when you turn on tap a little no hot water, tap needed to be on full.
Did consider a combi here, but in real terms it is a very small storage tank inside the boiler, and run from boiler to taps is further than run from cistern to taps, so delay would increase, and with a cistern we can have an immersion heater powered with an iboost+ so DHW heated in the main by solar so far cheaper than running the boiler, and to have a store in the boiler clearly the boiler is larger, and already the oil boiler we have is a large lump on the kitchen floor.
I have considered a small heater at the front kitchen, the back kitchen seldom used, but each one I have looked at is a large lump taking up room in some kitchen cupboard. And I am short on storage. So only real need for warm water is to wash hands, boiling water is from kettles, I looked at things like this
but 3.5 kW so needs dedicated supply, this
hold 15 litres and is only 2 KW so would work, but then using electric at peak rate, and fills a cupboard. So although running off cold water to get the hot at the moment at least I am using oil or solar which must be cheaper to using electric at peak rate.
As to if supplied with a timer so heated over night only it would stay hot through the day not sure, 8.95p per kWh midnight to 8 am, and 31.31p per kWh during the day so not sure how this compares with loss of heat when using oil or gas, so is it worth it?
A £130 unit to save a few pence lost heating up the pipe work and boiler seems like cracking a nut with a sledge hammer. I had an instant gas heater for years, not a combi, two independent boilers next to each other, and I knew what needed doing, it needed the 22 mm pipe work removing and replacing with a smaller bore pipe, as at mains pressure no need for large bore, and the pipes needed lagging, but looking at £100's to do the work, to save a fraction of a penny each time used, I look at what I have done with this house, and wonder was it worth it?
I had the iboost+ fitted when the solar panels went in, I have 6 kW of panels, and 3.2 kW of storage, and electric costs between £1.50 and £3.50 per day, around £2 most days, my direct debit per month has gone down by £30 but spend over £10k so 27 years to break even, I seem to have got it wrong? Was told around 6 years to get pay back, so at £139 per month saving I would break even, but was only spending £119.70 so would need to get £20 a month for my export to get it back in 6 years.
So don't make my mistake, do your maths first, likely not worth doing anything.
