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Our heating system temperature and hot water are not independently adjustable
If you have zone valves you should be able to limit the HW temp to 60 and limit the CH temp to whatever you want. If you don't have zones even for HW then you should fit them.
Some other thoughts besides the FHT stuff (which I also have). These are the things that will save you the most money.
- you need HW priority if you are going to have different temps for HW and CH (may require a relay)
- use an aquarium thermostat on the HW cylinder (plus the safety cutoff overheat stat if you have one). An aquarium stat allows digital setting of degrees to 1/10th degree, and also setting of the hysteresis. Unlike the crude things sold by plumbers merchants. £10 on ebay. Less heat wasted from the tank as it is safe (>=60) but cooler than it might have been.
- extra lagging on the HW tank. A big one like yours loses 2kWH/day even with the built-in lagging. The fact that it feels cold is no guide. Mine is in a Kingspan box with extra lagging (wool-based from B&Q) around it.
- perhaps even a tempering valve on the HW outlet to mix with cold, thus making the tap temp cooler/safer/less likely to scald.
- use a weather compensator. This reduces the CH flow temp as the outside temp rises. I'm assuming your boiler is a condensing boiler (it should be for decent efficiency). Reducing the flow temp avoids wasted heat, keeps the rads on cooler but longer, and makes the condensing process recover more latent heat. You can buy them but I made my own.
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