My oil-fired combi boiler sits in an outside 'boiler room'. Basically a small, purpose-built lean-to with a slate roof.
The room is insulated, but I still think it must waste a great deal of heat, especially in the summer when the heating is switched off and only the hot water is left running.

The wasted heat I think comes from the need to heat a buffer tank. Is there a way to switch this feature off or bypass it completely? I know this would mean waiting for longer for the water to heat when having a shower, but I'm willing to live with that and use the kettle for most hot water needs.

The boiler is a 15 yr old Grant Vortex Outdoor Combi.

I had considered directly insulating the boiler, but I guess that could overheat the components and lead to speedy boiler death?!

Anyone?

There is only one thermostat dial on the boiler and as I understand it this is to set the temperature of the water going to the radiators. So I don't think this affects the buffer tank temperature.

Edit: Meant to add...that thermostat is already set to lowest.

Certainly considered a hot water cylinder, but...
- Not much space (some space for a horizontal type in the eaves but then I lose useable space).
- I'm hoping I can dump most of my spare PV into my EV.
- I think it would take a loooong time to claw back the outlay for a plumber to hook up a cylinder, shower & under counter heaters.

So for now I'm stuck with my combi but trying to reduce use and reduce any wasted heat (which I suspect is more than the actual use!). If no solutions regarding the buffer tank then I may resort to switching the HW off and on as and when required. Bit of a pain though.

I think the heatslave tank (little tank inside the oil boiler) helps reduce short cycling of the oil boiler. Gas boilers can cope with this better. Oil boilers don't like it at all. If you by pass this heatslave tank, every time you turn on the hot tap for even a few seconds, the oil boiler would fire up.

Inefficient short burning would likely consume a lot of oil compared to the heat output, soot-up the oil jets etc of the boiler, and so potentially be more costly (inefficiencies and higher maintenance costs) than anything you might possibly save in terms of lost heat.

GarethJ suggestion of a timer could work, ie. timed-off when you're out/asleep, but that risks no hot water on some occasions when you want it, so would need the boost function.

If you're up for a bit of tinkering, relocate the heatslave tank outside the boiler housing, and super insulate it. Extend the pipes a few hundred mm, so it's adjacent to the boiler, but room for insulation wrap. How much heat are you losing in the pipework delivery to your taps? More of an issue I'd guess than the heatslave tank losses.

No solutions really, but may avoid inadvertent worsening of inefficiencies.

If you use single leaver taps always have them to the cold side unless you actually need hot/warm water. To often single levers are left in the mid position which means that any small mount of water drawn off takes some hot which will never get to the taps and so is a total waste.

Thanks for the suggestions all.
With regards mixers, we always use full cold and even have it drummed into the kids. :-) Pretty tough when the water is about 5 degrees in the winter!
For doing dishes we generally use the kettle.
So main hot water use is for showers. Hence, my annoyance of heating the entire boiler room 24/7 just for this.

Not sure how I can calculate the loss with any degree of accuracy, but given the temperature of the little boiler room when I open the door (around 30-35 degrees I'd say) I'd say it is significant.

I think I read that the 'buffer' or 'pre-heat' water is actually within the heat exchanger, so I'm not sure how easy it would be to isolate and insulate that. I suppose the critical bit is wherever the sensor is. Got me thinking though and I'll review.
It does seem crazy that a constant pre-heat tank wouldn't be insulated in the first place. Hope the situation is improved on newer boilers!

There is a switch on the boiler and also a fused switch adjacent to the boiler... but the boiler room is round the back of the house. I may look into routing a switch.
If I look at insulating the pre-heat tank then what is the best insulation to be quite thin and cope with high temps? Is this a job for aerogel??

A boiler programmer would probably be a neat solution. Cheap enough and kind of made for the job with 7day programming. Obvious location would be between the supply and the boiler but could be operated from a different/more convenient place with some wiring or widgets.

Some oil boilers are incredibly full of steel. If it's in the heating season and the machine is in the house it's not so bad but I understand your predicament - it's a huge mass to heat for a few hand washes and, being integral to the machine, is hard to safely extra insulate without risking cooking other boiler components. Though having said that, I did put a bit of extra insulation around the top and sides of my system oil boiler.