Under sink water heater

For the purposes of this discussion, pressurised = unvented.

On most models, you do not require special taps. It's just a mini-megaflo. Mains CW in, HW stored at pressure, mains pressure HW out.

There are some stranger models around. These are un-pressurised, yet provide mains-pressure HW, and work like this:

Mains cold comes in, to the tap in the first instance. The tap does not open directly to the spout, it opens to a return pipe to the cylinder. The tap then opens the CW supply to the cylinder. This then forces the stored HW out a seperate pipe to the spout, at mains pressure. In this config, the cylinder is not pressurised, it is open to the spout at all times. The pressure is only applied when the cold supply is turned on.

These require a special tap ( with a return pipe to the cylinder. )

Sounds like the plumber probably knows what he's doing, and you ought to let him get on with it.

What Ron said :-)

I've fitted several of these - the pressurised ones, no problem, they work a treat.

And I've just had to replace one of mine- only 2.5yrs old but very hard water area... You can't replace just the element -immersion heater stylee-.

It was an Ultraheat which dont seen to be about any more- the new one is a Redring. (15l 3kw)

Tim..

And have the annoying habit of continually dripping, with people trying to turn the tap off harder, which makesno different to the dripping.

Owain

but knackers the washer, causing a genuine drip.

But eventually (sooner rather than later) nackers the tap.

That sounds like it's a unit that just escapes all the really serious regs. So you may fit it with out a G3 ticket, plug it into (a FCU on) a 32A ring circuit, no discharge or vent pipes required (it forces expansion upstream into the mains).

In message , Tim.. writes

Umm.. In an effort to avoid this, I installed ours in the *hot* water (softened) circuit.

The instructions were pretty insistent about expansion issues but I really could not see any extra safety concerns provided there was ample feed pipe length and no local shut off valves.

regards