how to set the Historesis on a gas hot water system

[Daveoak]

Would Anyone know how to reset or set the historesis on a gas Hot water system.
my hot water cools too much before it comes on to reheat.
I mean its almost tepid before it comes on, is it by the tank somewhere or is it by the gas heater, there is a box there to select the water temp, which is on full!!
or is it that I need to replace that box

 

[Agile]

You have not described your system but I am going to assume that you have a conventional system boiler and a hot water cylinder.

The temperature of the stored water should be set at about 55-60°C and controlled by the thermostat on the cylinder.

The boiler output temperature is controlled by the boiler stat and for water heating should be set at about 65-70°C.

If the cylinder stat is old, well poked or just not very good the on/off gap may be much more than the 3-5°C to be expected when new.

If you want to check/set these parameters then you will have to have a digital contact thermometer and know how to use it for this purpose.

Tony Glazier

 

[ChrisR]

SLightly complex subject. Hysteresis on many a cylinder stat is very wide indeed, far more than a couple of degrees.
You can get elecronic cylinder stats, some I'm sure I've seen where you can adjust things but those may have been industrial.
If you use thermally conductive paste tween stat and cylinder the effective H drops quite a bit.
One complication is that stratification from base to top of cylinder might be say 15 degrees, - what are you trying to achieve... Secondary circulation loops do many things, including evening out the strat.

 

[Agile]

Stratification effects are reduced if the boiler output temperature is carefully set to be no more than say 10 °C above the hot water storage target temperature.

Of course that is good with a condensing boiler but creates difficulties with a standard boiler if heating is required to be at 80 °C.

It also increases the HW reheat time if the boiler is set correctly for water heating!

Tony

 

[Daveoak]

Sorry for the delay in coming back. Thanks for all the input...
Now it seems that I need to tell a few details so that maybe someone can advise me.... the Tank is a 180 Litre TURBUNE PREMIER made by IMI Heating, thats upstairs and there is some kind of panel on the top.
The Actual Gas heater is downstairs off the Kitchen, and all it says on it is that it an IDEAL CLASSIC. It has a temperature control knob on the front thats allways been set on full.
other info i'm not a plummer so please speak in terms I will understand.

Thanks Very much

Dave

 

[ChrisR]

Not sure what further advise we can give, other than to
1) speak to the manufacturer of the cylinder and
2) invest an a digital surface and liquid thermometer.

If you want a constant output hot water temp you could use a thermostatic blender (mixing valve), whch will hold it to a degree or so. See Reliance or Altecnic.