Uncombining a Combi?

[PTH]

With a recent house move we have inherited a, recently installed, Worcester 24cdi combi. This seems to have been properly installed (Benchmark etc.) with the possible exception of the flue, more of which in a bit.

We are planning some fairly significant changes to the house, part of which will involve moving the boiler as the flue route clashes with our proposed stair location.

I was going to take the opportunity to add in a gravity fed hot water cylinder to serve the bathroom so that we don't need to plan baths several hours in advance. Further thoughts on this are "why not put the kitchen on to the cylinder as well" - I like to have the hot tap dribbling when washing up to rinse off the soap which isn't really possible with a combi.

Now, all of this is effectively taking away the domestic hot water function of the boiler all together. Do any of the boiler fitters out there have any opinions on this? If necessary, I could leave the hand basins or the shower on the combi to give it something to do now and then....

To get back to the flue, as it is installed at present the flue length is about 6.5m vertical ie. 2m in excess of the MI. I believe this is responsible for the excessive pluming I have noticed in cold weather, the flue gas being 'overcooled' by heat exchange to the incoming air. If I move the boiler it will shorten the flue length to about 2.5 m. Can anyone confirm my theory that the plume will be reduced?

...And before you CORGI people start - although I feel competent to do this work, I just don't have the time so I will be getting a local registered installer to do the boiler, flue and gas works.

Thanks.

 

[kevplumb]

dont think a gravity system will work usually fully pumped

wouldnt be a bad idea to leave something connected to the hot
last one i did combi fed the kitchen and utility
cylinder fed the bathroom

 

[PTH]

Thanks Kev, my reference to gravity fed relates to the secondary side, I'm planning on using the pumped radiator circuit for the primary coil. I will just turn off the radiators, except the bathroom one in the summer.

 

[DP]

Pump is within the boiler. The pump usually starts the boiler sequence with terminates with burners lighting. To get the burners to light (to get the gravity zone to function) is not possible with a combi. These boilers are low water content beasts- I suspect any boiler with copper heat exchanger (low water content), cannot be used with gravity sytem. I could be wrong on that. Furthermore, why go backwards as gravity HW system is sluggish to heat and a no no with regard to BR Part L

 

[PTH]

Sorry if I'm being misleading here:- When I mention gravity fed I am referring to the domestic hot water ie. high level cold water storage tank, indirect cylinder and all outlets below it - hence gravity fed as opposed to unvented, mains fed. The primary pipework will be pumped, using the pump in the combi. I have no intention of using a gravity (thermosyphon) heating system, although I have designed a few in the past for large buildings.

 

[DarkInferno]

I had somthing simalar to this a few months ago, a EcoMAX (28KW I think)

Plumb the cylender in as a S plan style (include an auto bypass), and fit an external clock.

That way you will be able to keep control over HTG/DHW.


If possible try to retain as much of your hot water on the combi, as you will have far greater efficency as it has less heat tranfer loss.

 

[PTH]

Thanks Dark..
The shower works really well from the combi ar the moment as long as no toilets are flushed or taps opened within a 5 mile radius so I'll keep that and perhaps the washing machine on the combi and use the cylinder for the rest, with S-plan as you suggest - I'm sure I have an auto bypas valve somewhere in the box of oddments.

I don't believe the efficiency argument is that strong anymore - modern insulation on domestic cylinders is so good that I would even consider running a pipe coil round the cupboard for airing.

Anyone got any thoughts on the flue?

 

[COG]

Had a 24cdi doing the same thing until boiler repositioned to a 3.5M flue, allso reduced the hunting when on high fire. best keep something running on the dhw circuit to avoid build up of sediment/corrosion.