Hot water tank thermostat

330d

Recently moved into a house which has a system boiler and hot water cylinder setup. Previously I always had a combi boiler.

The hot water cylinder has a thermostat, am I right in saying the boiler will kick in when the water temperature gets below the temperature set on the thermostat?

Alter_ego

Yes, subject to any timer in the circuit being "on"

330d

Thanks. So if no timer is on, then it the boiler won't kick in?

Or in my case, I have the boiler schedule to come on 8-9am and 8-9pm. 

Alter_ego

It's possible to wire it either way, why not just try it

canaldumidi

So between 8-9am and 8-9pm the boiler will kick in if the cylinder thermostat registers lower than the required water temp. Or of course if the central heating calls for the boiler to kick in! Is the central heating programmed for the same hours as the hot water?

Outside those hours, the cylinder stat will have no effect.

Belenus

330d said:

Thanks. So if no timer is on, then it the boiler won't kick in?

Or in my case, I have the boiler schedule to come on 8-9am and 8-9pm. 

Does your timer have the options to select between CH only, HW only or both?

knightstyle

Usually the timer switches on the system and the boiler first heats the water to the temperature set on the tank thermostat, when the temp. reaches the set level the boiler changes to heating the radiators.
In very cold weather I used to lower the tank temperature in the evenings so the boiler would heat the house as soon as the timer switched it on as we mainly used hot water in the mornings.

Rodders53

knightstyle said:

Usually the timer switches on the system and the boiler first heats the water to the temperature set on the tank thermostat, when the temp. reaches the set level the boiler changes to heating the radiators.

Not on any decent system boiler install I've ever had.  Even the 'horrible' 3-port valve systems allowed CH, HW or both (mid-position) to operate at the same time.

Yours would be an ancient W plan installation, and is, nowadays, very very unusual.  Albeit we have no real idea what is installed in the OP's home so may need pics etc., to identify.

https://www.warmzilla.co.uk/blog/s-and-y-plans-explained

Section62

knightstyle said:

Usually the timer switches on the system and the boiler first heats the water to the temperature set on the tank thermostat, when the temp. reaches the set level the boiler changes to heating the radiators.
In very cold weather I used to lower the tank temperature in the evenings so the boiler would heat the house as soon as the timer switched it on as we mainly used hot water in the mornings.

It depends how the system is installed and the timings set on the programmer.

With a Y or S plan system if both the hot water and CH thermostats are calling for heat when the timer comes on then both can be heated simultaneously to start with.

If the programmer allows separate switching of HW and CH then either could be set to come on independently at different times - personally I set the CH to come on about 15 mins before the HW (if heating HW by the boiler) so the bulk of the circulation water is 'hot' before it starts circulating through the HW coil.

Belenus

Rodders53 said:

knightstyle said:

Usually the timer switches on the system and the boiler first heats the water to the temperature set on the tank thermostat, when the temp. reaches the set level the boiler changes to heating the radiators.

Not on any decent system boiler install I've ever had.  Even the 'horrible' 3-port valve systems allowed CH, HW or both (mid-position) to operate at the same time.

Yours would be an ancient W plan installation, and is, nowadays, very very unusual.  Albeit we have no real idea what is installed in the OP's home so may need pics etc., to identify.

https://www.warmzilla.co.uk/blog/s-and-y-plans-explained

Our 2004/5 Potterton Powermax HE 150 does not allow CH and HW at the same time. The valve switches between CH and HW and there is no mid way position for both at the same time.

This doesn't bother us as the 150 litre tank is so well insulated that we only heat it up for about 15 minutes every other day or so.

It has HW priority. When we return from holiday or time away in winter to a cold house, we switch the CH on and make sure the HW is switched off so that the house heats up quickly and the boiler doesn't spend the first 20 minutes or so heating up water leaving the radiators cold.

Belenus

Section62 said:

knightstyle said:

Usually the timer switches on the system and the boiler first heats the water to the temperature set on the tank thermostat, when the temp. reaches the set level the boiler changes to heating the radiators.
In very cold weather I used to lower the tank temperature in the evenings so the boiler would heat the house as soon as the timer switched it on as we mainly used hot water in the mornings.

It depends how the system is installed and the timings set on the programmer.

With a Y or S plan system if both the hot water and CH thermostats are calling for heat when the timer comes on then both can be heated simultaneously to start with.

If the programmer allows separate switching of HW and CH then either could be set to come on independently at different times - personally I set the CH to come on about 15 mins before the HW (if heating HW by the boiler) so the bulk of the circulation water is 'hot' before it starts circulating through the HW coil.

Ours (see above) does that.