Combi boiler and unvented HW Cylinder

[Edward]

Hi all. Just after some advice/opinion to my setup as it slightly confuses me.

 

We have a Worcester 8000 Life combi boiler. We also have a hot water cylinder in the loft. Given the boiler has both separate heating and hot water outputs, I would have assumed the hot water cylinder would have been fed from the hot water feed from the boiler whilst the heating for the rads would be fed from the heating output. Instead the heating for the hot water cylinder is on the same circuit for the central heating system. Is this correct? Is the hot water function only for hot water on demand?

 

I am asking because i have turned down the flow temperature from about 70 to 55 degrees to a) reduce the energy usage and b) ensure return temps allow condensing to happen. However in doing so the hot water cylinder will never get to safe temperature (legionellas). 

 

Advice welcome

[JohnMo]

A combi without the DHW bit connected becomes a system boiler.

 

Is DHW fed from the cylinder or Combi, the cylinder could be a buffer?

 

Some photos may help

[Edward]

Combi boiler heats water, which in turn heats cylinder and therefore DHW is fed from the cylinder.  

[JohnMo]

1 hour ago, Edward said:

(legionellas)

Do a Google search and search on here, many opinions.  Think I read a fairy rounded report on heat geek.  Looked at all the sources and different storage temperature.

 

[PeterW]

1 hour ago, Edward said:

. We also have a hot water cylinder in the loft.

Vented or unvented..? And is it really connected as a combi would indicate not. I have seen it where they have combi flow to the kitchen taps but the rest is off the tanks.

 

quickest way to check is go round running hot taps and then see what causes the boiler to fire - should show what is on the tank and what is on the boiler direct 

[Edward]

Unvented. The HW taps are not connected to the HW output. The plumber confirmed the hot water control on the boiler doesn't do anything, as nothing is connected to it. Thus the HW taps are draining the cylinder, which in itself is a PITA because its a sizeable house and the taps take forever to heat up, wasting HW in the process. 

[JohnMo]

A combi takes longer, so that's maybe a reason for the cylinder in the first place.

[Nickfromwales]

On 12/12/2022 at 16:59, JohnMo said:

A combi takes longer, so that's maybe a reason for the cylinder in the first place.

Not if it's on 22mm pipework and it's in the attic? It'll take much longer to arrive from there.

 

On 12/12/2022 at 16:41, Edward said:

The HW taps are not connected to the HW output. The plumber confirmed the hot water control on the boiler doesn't do anything, as nothing is connected to it.

Is there just an unused pipe left at the underside of the boiler?

[Nickfromwales]

Why has a combi boiler been installed instead of the system version?

[ProDave]

On 12/12/2022 at 14:07, Edward said:

However in doing so the hot water cylinder will never get to safe temperature (legionellas). 

We have discussed before, an unvented HW cylinder fed with mains water, there is no way for bugs to get in, so no need for a high temperature.  Mine heats to 48 degrees only.