HW Cylinder Thermostats

[Schmill]

Just a quick one, (hopefully).

I'm just wondering if there is a better sort of HWC(ylinder) thermostat than the one I currently have.
The current one seems slow to react, and as such the HWC is often almost completely empty of water that is of a reasonable temperature before the thermostat 'realises' that it's cooled down and needs to switch on.

The stat I have is held against the copper of the cylinder in an area where the covering insulation has been scraped away. When I released the strap It can be seen that it is effectively a metal frame that sits against the cylinder, and within the frame is a bi-metal based switch, so it it actually sensing the air temperature close to the cylinder, rather than the actual cylinder itself.

Are there any more 'modern' stats that perhaps monitor the temperature of the copper itself? Would that work better?
Also where abouts should the stat be on the cylinder? This one is positioned somewhere between 1/3rd and 1/2 way up the cylinder, which seems high to me? (Presuming it wouldn't react until the cool water reaches the area of the cylinder it is strapped to?)

Thanks

 

[JohnD]

(Presuming it wouldn't react until the cool water reaches the area of the cylinder it is strapped to?)

That is correct. There is no point in putting it lower than the Coil (look for the primary entry and exit connections on the side of the cylinder)

A modern boiler will heat a modern cylinder in about 20 minutes, and faster than most normal usage except a bath tap or power shower.

If you have the stat low down the boiler will fire up frequently for short periods, which is uneconomical. I have mine up high and the boiler heats up a full cylinder; then nothing until I am nearly out, then another full cylinder. This is economical provided your cylinder is big enough for your pattern of usage. Do you think yours is?

 

[Schmill]

So it sounds like everything is in the right place and the thermostat is correct.

This is economical provided your cylinder is big enough for your pattern of usage. Do you think yours is?

No

Our old power shower used to run out of water quite quickly, (2 or 3 showers, depending how long people took).

The new bath is quoted at 210L capacity.
The HWC is 450x900 which works out at 117L for an indirect cylinder.
Also we will be installing a new power shower soon, (when the rest of the bathroom is done).

I guess I was hoping that there was someway I could get the existing cylinder to 'recover' quicker, but it sounds like there is not. When running a bath the water can be running for quite some time before the boiler fires up. I guess it's just a case of putting up with it for now then until we can afford a bigger cylinder

Thanks anyway

 

[JohnD]

you can move the stat lower if you want.

but it must be a shade higher than the bottom entry of the coil on the side of the cylinder.

and save up for bigger cylinder.

 

[stem]

The stat I have is held against the copper of the cylinder in an area where the covering insulation has been scraped away. When I released the strap It can be seen that it is effectively a metal frame that sits against the cylinder, and within the frame is a bi-metal based switch.

As a bi-metallic strip is a mechanical device, it will wear, if it's 10 years old or more it will be inaccurate, a new one may well improve things.

it is actually sensing the air temperature close to the cylinder, rather than the actual cylinder itself.

Not really. The metal frame is in direct contact with the copper cylinder wall and will conduct heat from it, so that it will reach the same temperature as the cylinder. The frame also traps the air when it's in position (it's not open to the ambient air) and the cylinder insulation should come right up to the sides of the metal frame hence insulating it.

 

[Schmill]

The frame also traps the air when it's in position (it's not open to the ambient air) and the cylinder insulation should come right up to the sides of the metal frame hence insulating it.

Perhaps that is part of the problem then, rather than cut a neat hole through the spray-foam insulation on the cylinder to fit the stat into a great swathe of it has been sliced off, (imagine a blade being run down the cylinder at a tangent), so there is no insulation next to / near to the stat at all. I might see if I can pack some expanding foam or something around it if that will help? (Of course I'll look and see if I can move it lower first!)

 

[JohnD]

if you decide to move it, cut a neat hole that's a good fit. Usually if you do that, you can put the cut-off piece into the place where the stat used to be. Not in your case, though

Beware expanding foam is very sticky, and you will never get at the stat again unless you wrap it in polythene before squirting.