Hot or Cold water to outside tap

Instant water heater on the inside of the wall, and a power switch for it next to the tap?

Why electrically? It would no doubt be possible but it would seem to add a lot of complications.

Why not just use a three way valve? Like this maybe?

Tim

Possible the cheapest source of electrically controlled valves would be from a scrap washing machine.

You should probably also make sure you fit non-return valves to prevent any chance of back-flow.

Chris

Is that possible with a combi?

Tim

Possibly not but water regs will want a NRV on the outlet or if easier on both feeds.

But with no storage tank, it makes no sense at all. Not saying that you're wrong but who is going to come out and check for NRVs? ;-)

Tim

Why not just tee off the hot supply and pipe it to a separate outside tap?

Either a three way valve for central heating or a couple of one way valves (motorized). They are generally 22mm, so you'll need reducers. But if they are used infrequently, may stick.

Is your water hard? They may not like a continuous flow of fresh hard water through them - being more designed for a 'sealed' system.

You'd also need one a one way valve in the potable water side.

NT

I'll repeat my question, how could this happen with a combi?

At most there may be a wee bit of backflow from cold to hot if the hot supply pressure is regulated lower than mains but with no tank to backflow to, the pressure would almost instantly rise to match.

One NRV on the three way outlet would prevent any mains contamination in the event of any back syphonage following a supply failure.

Tim

If he buys the rest of that valve (a standard 3 port) he'll be able to do it electrically :)

Which you should have anyway :)

Why wouldn't it be?

need mains to move em so you will need solid state switches or relays from lower voltages

Well I was thinking about mains cold into gravity hot (or even combi hot into gravity cold), neither of which will occur in a combi system. I would agree that according to regs you should have a NRV to protect the mains supply from back syphonage in the event of mains supply failure.

Tim

The pipes and any tap/valves on the inside will be in quite an inaccessible place for day to day access.

As I said earlier, tee off the hot supply and run the pipe to another outside tap next to the cold one (if poss). The new outside tap will have a NR Valve fitted integrally. No electrics involved.

Pair of single valves would be better then IMHO - both off for winter.

In theory, contaminated water from the garden can enter the mains supply. Not very realistic but..... The chance of being inspected is close to nil unless the water board are on the property for some other reason.