On Sat, 01 Apr 2006 15:51:28 +0100, in uk.d-i-y Ed Sirett
wrote:

If I can elaborate on Ed's advice ...

On Fri, 31 Mar 2006 23:45:07 +0100, t wrote:

We are in the process of having central heating installed, replacing an old
partial system. We have done this before in other properties so know
something about it. This property has 11 radiators. We are using a Honeywell
CM37z system with radio-linked TRVs on every radiator except for the
bathroom where the steam may corrode the electics of the radiator head.

Under the new Building Regs, Part L, this is no longer sufficient. You
must have a separate timer for the hot water (perhaps you have done
this) if the whole system is being replaced.

See "Heating controls" in
http://portal.est.org.uk/uploads/doc...dings/ce53.pdf

What should I read? Has anyone any references? Any input would be most
appreciated

The Honeywell guide summarises things reasonably well
http://content.honeywell.com/uk/homes/Regulations.htm

[snip]

The bypass is almost certainly needed to provide a path for primary water
to continue after the demand has ceased. The boiler will need this (some
have this device internally so no need to add an extra one on the pipework).

Indeed. For example, from my daughter's Ariston EuroCombi A/23 - A/27
MFFI Installation Manual ....

"By-pass: The appliance includes an automatic by-pass valve, which
protects the main heat exchanger in case of reduced or interrupted water
circulation through the heating system, due to the closing of
thermostatic valves or cock-type valves within the system."

This requirement to have a by-pass valve (not necessarily automatic)
stems from the boiler manufacturers installation requirements rather
than from 'regulations'. However, the new "Basic and Best Practice
Specifications" calls for an automatic valve to be used, rather than the
old way of a fixed gate valve.

Central Heating System Specifications (CHeSS) - Year 2005
http://www.est.org.uk/download.cfm?p=1&pid=544

"An automatic bypass valve controls water flow in accordance with
the water pressure across it, and is used to maintain a minimum flow
rate through the boiler and to limit circulation pressure when
alternative water paths are closed. A bypass circuit must be installed
if the boiler manufacturer requires one, or specifies that a minimum
flow rate has to be maintained while the boiler is firing.The installed
bypass circuit must then include an automatic bypass valve (not a
fixed-position valve). Care must be taken to set up the automatic bypass
valve correctly, so as to achieve the minimum flow rate required (but
not more) when alternative water paths are closed."

The valve must be 'smart' not simply a gate valve on a piece of pipe with
the handle removed.

Only needs to be smart in the sense that it opens according to the water
pressure across it - doesn't need any fancy electronics. e.g.
http://www.danfoss-randall.co.uk/def...lt=tem1019.asp


Phil
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