My boiler hot water and central heating on same loop??

CaptainComedy · 5 Jan 2017 at 18:32

Hi all,
I have a weird scenario, please refer to the below pic:

I was always under the impression my worchester bosch controlled hot water and central heating differently. I have a hot water tank which connects to it so we always have hot water and now that it's winter, I have turned up the central heating to get a bit more warmth... but in doing so, the hot water temperature has also become a lot hotter!

I turned the hot water dial down to what you see above, and it has no effect on the taps... now what I am wondering is, if the taps are affected by the radiator:

what is the hot water connected to?
what have I been drinking from?
what is the tank connected to??

any advice appreciated :S

robj20 · 5 Jan 2017 at 19:16

The same water that goes round your central heating goes through a coil in your hot water tank. The water tank gets fed by mains water and is this that comes out of the hot tap.

There will be a valve somewhere that can either send it all to the central heating or all to the tank coil, or to both.

CaptainComedy · 5 Jan 2017 at 20:39

so what's the point of the right knob??

Dangerous Dave · 5 Jan 2017 at 21:37

CaptainComedy said:
so what's the point of the right knob??

If you use Worchester timer/thermostat controls you can set different flow temperatures for the heating and hot water which would allow you to run the radiators at a cooler temperature to allow the boiler to condense for longer periods.

A boiler only condenses when the flow return temperature is under 56c, you generally need the flow around 70-75c to heat a hot water cylinder to 60c with the flow in the 70s the return from the heating circuit is likely to be over 56c which would mean the boiler is not condensing which reduces efficiency by approx 10-12% which results in it using more gas.

Dangerous Dave · 5 Jan 2017 at 21:45

You mention the hot water getting hotter you should have a thermostat on the cylinder to set the temperature of the hot water supply to the taps which should be 60c + to prevent bacteria build up in the stored water, the flow temperature from the boiler then needs to be 10-20c higher than this to allow the set target to be met.

CaptainComedy · 5 Jan 2017 at 22:14

this makes me a sad panda...

how can if I have a Worcester timer / thermostat? my thermostat doesn't have a Worcester Bosch logo on it... we had it same time as the boiler (year and a half ago)

blueboy2001 · 6 Jan 2017 at 00:17

The HW control know is unused in your installation. Worcester sell an optional diverter valve kit which when used alongside their controls, allows the boiler to control whether the output goes into the CH or HW circuit, and as such allows you to select the temps independently.

The valve and controls are more expensive than say a Honeywell programmer and motorised valves, so more often than not the cheaper stuff goes in.

The new build estate I live on have installed WB weather compensators with the boilers, but they've fitted Honeywell controls and valves. They've ended up having to disconnect all the weather compensators because when it's warm outside the boiler drops the flow temp to about 40 degrees and you end up with lukewarm hot water! Whoever specced them failed to realise they're absolutely useless without the optional diverter valve fitted.

CaptainComedy · 6 Jan 2017 at 20:32

blueboy2001 said:
The HW control know is unused in your installation. Worcester sell an optional diverter valve kit which when used alongside their controls, allows the boiler to control whether the output goes into the CH or HW circuit, and as such allows you to select the temps independently.

The valve and controls are more expensive than say a Honeywell programmer and motorised valves, so more often than not the cheaper stuff goes in.

The new build estate I live on have installed WB weather compensators with the boilers, but they've fitted Honeywell controls and valves. They've ended up having to disconnect all the weather compensators because when it's warm outside the boiler drops the flow temp to about 40 degrees and you end up with lukewarm hot water! Whoever specced them failed to realise they're absolutely useless without the optional diverter valve fitted.

So is it a good idea for me to get the Worcester Bosch valve and controls fitted? baring in mind I want this to be part of my smart home setup so will eventually buy a nest (which is another kettle of fish)...

Thanks for the advice btw

blueboy2001 · 7 Jan 2017 at 19:15

Fitting the diverter valve will mean running another pipe from the boiler to the HW cylinder, how straightforward that is depends on where the boiler in installed.

The Worcester controls are quite good, and they do their Wave smart range which may be worth looking at.

It's up to you whether it's worth it. Generally you can control the HW temp with the cylinder thermostat which should be mounted on the tank. If you don't have one, get one because they're cheap and it'll allow you to control the water temperature so you're not wasting gas. It may also allow you to turn the boiler down because if the HW is on sometimes you'll get the HW cylinder removing most of the heat from the water because there's less resistance than in the heating circuit. I usually put the HW on half an hour before the heating which is enough to heat the tank and then the boiler can service the heating alone. I run my boiler at 65 degrees. You don't want to drop below this because there is a small risk of Legionella at lower temps.

In a new install with alongsde a weather compensator and controller which can dynamically alter boiler flow temps depending on the outside temperature it will save you money on fuel, but the cost of such a setup is a few hundred quid so the payback time is like 10 years.

CaptainComedy · 7 Jan 2017 at 20:17

my boiler is right next to my hot water tank, they are in the same small room (I converted the old downstairs toilet into a boiler room) so I guess it shouldn't be difficult for the plumber...