In an earlier contribution to this discussion,
Mark Trueman wrote:

Hi all,

Yes, it may be the first failed diverter valve of the year, and it has
inspired me to thing about replacing my whole system. Firstly a bit of
background about the current system.

House is a 2 bed end terrace, currently only has 5 radiators, one in
the lounge (open plan to dining room), one in the kitchen extension
(which gets really cold in the winter - insulation problem there i
think), one in the master bed, one in the hall and one in the
bathroom. Second bedroom doesnt have a rad. They are all old rads, no
TRVs or anything. The system as a whole is absolute crud. Some of the
rads are in series with each other, some (in the kitchen extension)
are teed off. Hot water is heated indirectly in a standard cylinder
in the second bedroom airing cupboard. Theres a pump and a diverter
under the floor(!!!) in the dining room, by the Baxi back boiler. As
SWMBO wanted laminate, thats the replacement of that scuppered. I
dont even think its all plumbed in right, you have to have the hot
water on for half an hour before you have the heating on in order to
get any hot water at all. I think that the hot water is pumped
through the rads before it heats the cylinder water, so its cold by
the time it gets there!!

Our only requirements of the new system are....

6 new radiators and pipework that must be hidden underfloor
(floorboards and joists), sized to handle our heat requirements.

Keeping the ability to store hot water in the cylinder - two reasons
here which i think are valid - 1. our venturi shower wont work without
a hot water cylinder. 2. The wife likes the occasional bath.

I am umming and aahing about whether to do this diy, as it needs to be
in before it starts getting really cold, and working full time, i dont
have much of it spare to do something like this. And of course, i
havent done a central heating install before. Im confident that my
plumbing and electrical skills are up to it though.

Also, i need to keep the cost around the 1500 mark.

So on to my questions and musings.....

Can i easily keep the current indirect heating system used for our hot
water, while replacing the central heating section. Can a
combi/condensing boiler do indirect water heating efficiently.

Pipework under laminate floor - any suggestions. I think removal of
aforementioned minging flooring is the best option.

TRVs/Thermostats etc... We just want the whole house to be warm, not
really bothered about upstairs being cooler than downstairs etc. Whats
the best way to do this. Im guessing at trvs on all rads (except
bathroom one), but would you recommend a room thermostat in the lounge
to tie in with these. If someone could explain the need for room
thermostats when you have trvs i would appreciate it (seen a few
installs with trvs and thermostats but dont really understand why you
need thermostats when the temp is controlled by the trvs)

Types of boiler/boiler recommendations that fit in with our budget
would also be appreciated.

Im sure there are a load of things ive missed out, but any pointers
would be appreciated (and yes, i have read the faq etc)

Mark

It sounds as if you currently have a diverter valve (as opposed to a mid
position valve) and that it is set to heating priority - which is unusual. A
diverter valve gives you either HW or CH but never both at the same time. A
mid-position valve looks very similar - and can provide just HW or just CH,
but can also do both together when in its mid position. At very least you
should replace the diverter valve with a mid-position valve. From what you
say, the pump and valve are inaccessible, under the laminate flooring. You
need to do something about this *urgently* - either by moving them or by
creating some sort of access hatch. These are the two components which most
frequently need to be accessed whenever you need to do any trouble-shooting!

Do you need to replace the existing boiler, or does it have enough capacity
to supply additional radiators? You would certainly get better efficiency
from a new boiler, but this will involve a lot of plumbing because it seems
that all the pipework currently leads to the existing boiler site.

You can use the CH side of a combi to provide both CH and stored hot water
if desired, using zone valves (similar to your current setup) but there is
only any point in doing this if you are also going to use the HW side of the
combi to provide instant hot water to some of the taps - such as in the
kitchen. Otherwise, use a conventional boiler.

With regard to room stats, you need a boiler interlock in order to satisfy
the latest energy efficiency regs. This means that when the house gets up to
temperature, the boiler must automatically be turned OFF. If you use TRVs on
all rads but *don't* have a room stat, the boiler will remain on - keeping
itself hot by cycling on and off via its internal thermostat even when no
external heat is required. You therefore need to have one room with a room
stat but no TRV on that radiator.
--
Cheers,
Set Square
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