On 08/06/2016 22:28, Chris Hogg wrote:
On Wed, 8 Jun 2016 21:45:14 +0100, F news@nowhere wrote:

On 08/06/2016 21:36, Chris Hogg wrote:
On Wed, 8 Jun 2016 21:21:16 +0100, F news@nowhere wrote:

On 08/06/2016 20:51, wrote:
On Wednesday, 8 June 2016 20:14:48 UTC+1, F wrote:
I'm looking to put our immersion heater on a timer. It's protected by a
16 amp fuse so I assume the timer needs to be rated the same. Many of
the timers I've found so far seem to be 13 amp, even though some claim
16 amp in the headline description.

Domestic immersion heaters are 3 kW maximum so a good quality 13 amp timer will be adequate.

The immersion heater must have a thermostat and all new ones should have a secondary safety cutout with a manual reset. The thermostat will be inside the cover of the immersion and usually slides into a pocket so it can be replaced without draining down the cylinder.

Thanks.

The immersion heater in question is at least 38 years old and will boil
the tank if it's left on!

The immersion heater in my late mother's hot water tank has a
thermostat, and it dates from 1960. It may just be that your
thermostat was never set properly, or the setting has drifted over the
years.

I'll investigate once I've plucked up enough courage to disturb the huge
amount of 'stuff' in the cupboard!

Meanwhile, anyone got a recommendation for a digital timer? Or do I use
a spare I have that is rated 13 amps and which I use for switching
lighting when we're away?

I would need to replace the present immersion heater switch with a 13
amp socket and put a plug on the heater lead to plug it into the timer.
Any problems there?

I went down the same road as you're going down, some years ago. My
existing timer was just a plug-in jobbie that plugged into a socket in
the airing cupboard, and the immersion heater plug plugged into that.
But I was worried about the current capacity of the timer, and when it
eventually packed up, I installed one of these
http://tinyurl.com/hawlk2t mounted in one of these
http://tinyurl.com/jpwz7eg . It also needs an isolating switch, a
pattress and a junction box. The Sangamo is an electronic controller,
wired in, so no plug and socket arrangement, and has 16A capacity
which, like you, I felt was important at the time. It's probably more
sophisticated than I need, as it's used just as an on/off timer at the
same fixed times overnight to take advantage of E7 electricity, but it
works OK and does the job. My only reservation is that the display is
microscopic and difficult to read unless you get close and have it
well lit, e.g. with a torch.

As an alternative to mine, you could try these purpose-designed
immersion timers, also by Sangamo http://tinyurl.com/jydsg3j Might be
simpler to install, easier to read, and has its own case. If I'd been
aware of them, I'd have gone for the PSD version, in the middle.

Thanks, the PSD would do the job for me but it's quite expensive
compared with the plug-in type! But, of course, you get what you pay for...

--
F