Please help - understanding my heating / hot water system

Fishandchips80

@QrizB from what I can see (it’s hard to tell), the black cables are running into the white box at the bottom (which is then connected to the Drayton box in the middle in this photo)

Fishandchips80

@matelodave this is really helpful, we will give this a try thank you! 

QrizB

That's a useful photo, thank you.

Normally I'd expect that white box to be a purpose-built wiring centre, something like this:

https://www.cityplumbing.co.uk/p/honeywell-home-wiring-centre-230-v-42005748-001/p/834330

The great thing about one of those is that it's clearly marked out with contections for all the important parts of your central heating system.

What you've got isn't one of those; it looks more like a double pattress box (the sort of thing you'd use for a socket, or an electric cooker connector) with a blank faceplate on it. So whoever opens it up will have a bit of a job to decipher what's going on inside.

DON'T OPEN IT unless you're comfortable with mains-voltage wiring, since pretty much everything here runs on 230v AC. I'd also take care around that white "chocolate block" connector at the bottom of the ohoto, as those wires might be live.

What we can see is that the Drayton controller and the Honeywell thermostat both connect into the white box. It's possible that, as @matelodave suggested, the Honeywell is controlling the heating and the Drayton is controlling the hot water.

If you turn the thermostat right down, so the heating stops, then use the "Advance Boost" button on the Drayton to switch it on, you might find that the heating stops but the hot water turns on. If so, you'll probably have solved the mystery.

Fishandchips80

Thanks @QrizB! So, if I tie the Honeywell thermostat down so there is no heating on, and hit Advance Boost on the Drayton - how will I know if the hot water has come on? (Sorry if that’s a stupid question, there just doesn’t seem to be an ‘icon’ for hot water to show that it’s on or off)

QrizB

The boiler will run, the circulating pump will run, and if you carefully place your hand on the copper pipes adjacent to the motorised valves you should find that the outlet from the HW valve is hotter than the outlet from the CH valve.

The valves themselves have indicators to show if they're open or closed. You can see the little metal tab sticking out near the cable, on the stock photo I shared and in the photo you took. The CH one should be in the "closed" position and the HW one in this "open".

molerat

The little light on the 711 shows if the water is selected on.  Press the boost button then the light should go off.  If you wiggle the little lever on the HW valve with the light on and the tank stat needing heat it should be loose, with the water selected off the lever should be stiff to move.  If you drop the flap on the front the SELECT button will cycle through the 4 choices of the little arrow on the screen.

Fishandchips80

That’s it! I think you’ve solved it @QrizB!
so if that’s the case, and the Drayton is controlling just the hot water, then the timed schedule we inherited when we moved in was heating the water for 12 hours a day! (2 hours in the morning, 5 hours in the afternoon, and 4 hours at night)
This must have been costing the previous owner a fortune, and would explain my high gas bill!
Now it’s a wait to see if we are right and if the changes I’ve made to the schedule settings make a difference on the next bill!
I can’t thank you enough for your help with this, I would’ve been still completely clueless without your help. 

And thanks to everyone else who contributed to trying to figure this out 

QrizB

I'm glad we've helped you work out how your heating and hot water works. Hope you can get the gas bill under control

molerat

Having the water on for long periods should not cost that much unless you are constantly running the hot tap.  I found that even having it on for up to 15 hours only used a maximum of around 15 kWh a day so 75p or £23 per month.  Check your bill and divide the kWh charged by the gas units billed, the answer should be around 11.

There should be a thermostat on the side of the tank, check that is not screwed up to max.

One thing to help with your understanding of how it all works is that those controllers do not turn the boiler on, they simply tell the relevant valve to open and the open microswitch in the valve motor head calls for heat from the boiler.  The HW on command should pass through the tank stat then on to the valve.

Fishandchips80

Thanks @molerat - oh no, that’s not what I wanted to hear 🙈 . So if it’s not the hot water being on so much that’s caused the bill to be so high, then it must be how much we’ve had the heating on (I really didn’t think we’d had it on that much, the house is never above 18 degrees - it’s an old house).
when you say 11 is what it should be - what do you mean by this 11? I understand how you’re saying to calculate the 11, but what does the 11 represent? Thanks