It lights for 2 minutes once an hour to warm the heat exchanger and 'optimise delivery time for domestic hot water to taps or showers'. The problem is that this is burning a small fortune in gas for a function I use once a day in the morning for a shower - all of my appliances heat their own water and I'm out of the house 14 hours a day 5 days a week. Is the normal functionality for a combi boiler?

(first one I've lived with) if not it could actually be worth replacing the boiler as this appears to be adding £400 per year to my energy bills. On page 5 of the boiler manual you linked to, it states: PRE-HEAT DHW pre-heat will be disabled during DHW off periods. So, you need to define some DHW 'off' periods (most of the time, evidently) and a few DHW 'on' periods when you expect to use it.

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Programming those is described on Page 8. The default is to run DHW 'on' from 06:30 to 00:00 (page 11) Edit: I have observed that most generalizations don't hold worldwide, so I did not start out with this one - but certainly the vast majority of North American 'heating and domestic hot water' (what you presumably mean by 'combi' - not a term we use) boilers simply run to keep themselves hot all the time - there may be a summer/winter switch which changes some setpoints, but the basic operation is to sit there being warm/hot as a default. So yes, I'd consider that 'normal' operation for such a boiler, if it hasn't got the time controls as described. And @RedGrittyBrick's suggestion is a good one, if a newer control panel is compatible with an older boiler.

The other change from older boilers we commonly see here is a LOT more insulation - according to the manual linked, your hourly burn is somewhat more frequent that expected, at least on the newer model - unless your boiler is located in a particularly cold place, that may well mean the newer models are better insulated (and/or, if you have not already done so, you may want to add insulation to the water pipes.) You might ask the manufacturer if there is a way you can add more insulation to (at least some parts of) the boiler itself without causing a hazard. We had a period (not entirely extinguished, but somewhat tempered by observed results now) when 'instant' hot water heaters, where only a pilot light, or sometimes not even that, was kept burning until water is called for, were all the rage.

'Observed results' include far less savings (.vs. A well-insulated tank-type hot water heater) than claimed, and relatively delicate heat exchangers and control systems which become expensive to maintain after a few years. Some folks still love the things - they still hold a certain attraction for me, but being off the natural gas grid, not much - bottled/tank-trucked gas (propane) is far a more expensive fuel source.

Product Information: The diverter valve is a device that only appears in combi boilers. It allows the hot water to be sent to the central heating (radiators, etc.) or to the DHW system (taps, etc.). This feature is what seperates a normal boiler from a combi boiler due to the fact that a combi boiler wouldn't require a cylinder to provide heating and hot water. We only have this part as fitting one appliance, The Ideal ESPRIT 2 24. If this isn't the model you have, please contact us before ordering so we can confirm this part is compatible.