Temporary use of instant water heater

28 Jan 2011
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United Kingdom
Hi there. Primarily because it is my 'home turf', I recently posted essentially this question in the Electrics forum. Although there has been a bit of interesting discussion,most of the replies related to comments about the electrical aspects (in a good few cases giving incorrect information), which is something I neither need nor want, so I thought I would see what you folks here can tell me ...

... I am working on a house in which the only hot water is currently that from a couple of ancient 'over-sink' instant electric heaters, either or both of which may be on their last legs. The situation will eventually be addressed, almost certainly by installing a combi boiler in the kitchen, but that could be many months, or longer, down the road, so I am considering temporary measures.

I'm considering temporarily installing a 'plumbed-in' electric instant water heater in the kitchen, probably of around 10 kW. That would presumably work adequately for the taps in sinks, basins and even baths (one at a time - although the flow rate into bath would be too low to be very usable) but I'm wondering if anyone knows whether it would also 'work' reasonably with mixer shower?

On the face of it, I see no reason why a 9.5 kW or 10.8 kW instant heater feeding a shower should be any worse than a 9.5 kW or 10.5 kW electric shower. However, discussions so far have suggested that 'safety features' in a thermostatic shower mixer may in some way present problems if fed from an instant water heater, such that I might need to use a 'manual' (rather than thermostatic) mixer. Is that the case?

There is already an (unused) shower circuit present, adequate for a 10.5/10.8 kW load, which was installed 'just in case' an electric shower was ever needed (which I doubt it ever will), so I could use that circuit for a water heater. What I'm suggesting would therefore require neither a 'new circuit' nor any electrical work in a bathroom, so would not be notifiable, at least as far as Part P is concerned - whereas the most obvious alternative (to install a cheap electric shower, and retain the over-sink/basin heaters) would be notifiable (if I were concerned about that). Furthermore, what I am considering would mean that all that would need to be done eventually would be to get the water heater in the kitchen changed to a combi, without any appreciable changes to pipework etc. anywhere.

Any thoughts/suggestions/advice/experiences?

Kind Regards, John
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