Running Hot Water with Heating

Kennywilson77

For some reason my oil boiler and programmer will only alllow me to run central heating with hot water selected on also. I can get hot water only but not heating only. 

Does anyone know if this is massively wasting energy? I have just fitted a pressurised hot water cylinder which has its own thermostat. 

My thinking is possibly that once filled to temperature HW won’t be using energy but I bow to knowledge.

And if anyone knows how get CH only I’d be interested to know 

dunstonh

Does anyone know if this is massively wasting energy?

It will depend on how well your tank is lagged and whether it cuts off heating the water when it is upto temperature.

Replacing the timer/controller is a relatively simple thing to do for a heating engineer.  So, you could consider that.

Kennywilson77

I just changed it now to a hive myself. When I select heating the time clock is sending the on signal ok but the boiler only fires up the second I turn on HW

tacpot12

The problem is going to be how the valves are wired. If you haven't changed how the valves are wired, then you will only be able to run central heating with hot water selected on. If you did change how the valves are wired, did you use the Honeywell Wiring Diagrams, and if so, which "Plan" did you implement? 

matelodave

You really need to understand how your system is wired.

Old gravity fed systems would heat the water when the time switch was programmed to heat water, however when it was set to heating, all the thermostat did was to control the pump and the boiler just kept running under control of the boiler stat. Some valved systems were also wire this way especially if it was a cheap and cheerful timer/programmer.

Later systems with motorised valves could be wired in different ways depending on the type of stat and what sort of valves you've got fitted so you have to understand how its configured to make it possible to control it to heat water or heat the house independently.

lohr500

Agree with matelotdave. You need to figure out how your system is configured. 

northernstar007

my old thorn apollo did the same, converted to a combi, best thing i did

Kennywilson77

“Old gravity fed systems would heat the water when the time switch was programmed to heat water, however when it was set to heating, all the thermostat did was to control the pump and the boiler just kept running under control of the boiler stat. Some valved systems were also wire this way especially if it was a cheap and cheerful timer/programmer.”

Kennywilson77

It was exactly as you described until recently we got a pressurised cylinder fitted 

Kennywilson77

Pressurised cylinder now fitted. Although this has its own stat my thinking is the boiler thermostat is still controlling water temperature too

doodling

Hi,

Most (all?) pressurised hot water cylinders require that there is a motorised valve controlling the flow of water from the boiler to the cylinder, controlled by a thermostat fitted to the tank.  This is a safety requirement so shouldn't be ignored.

Assuming that the cylinder has been competently installed then a valve will be present.  The issue will be that the programmer either cannot cope with separate control of heating and hot water (and therefore needs to be replaced) or (in the case of a modern one) it needs to be reprogrammed so that it allows separate control.  It may also be that the wiring needs to be modified to allow the programmer to control the HW valve.

In practice it won't cost that much to have it on all the time the heating is running as the heat loss from the cylinder should be low (although the photos show lots of uninsulated pipes around the cylinder - these need to be insulated as they will currently be where the most heat is lost).  It does save a little money to only heat the water just before the major use of hot water leaving the remains to cover for the rest of the day so that the average temperature (and therefore the heat loss) is lower.