I've been asked by my father inlaw to install 3 radiators for him. After
reading the boiler manual (halstead finest gold combi) am I correct in
assuming that we can still run the hot water after isolating the central
heating at the boiler inlet and draining it off? Also is it usual
practice to put inhibitor in via a radiator before/during refilling for
Do the same general rules (ie 15mm shouldn't serve more than 3 rads)
apply for using 15mm or 22mm CH pipework for combis as they do for
traditional systems? Any help and warnings very much appreciated.
Posted via Mailgate.ORG Server - http://www.Mailgate.ORG
On Wed, 3 Sep 2003 18:53:17 +0000 (UTC), "Jonathan Curtis"
This isn't so much an issue of whether it's a combi as whether it's a
sealed system. For sealed systems you can obtain inhibitor in gel
form that can be injected into a radiator (I do it when they are empty
rather than against the pressure when full). Alternatively you could
put in a tee, a valve (e.g. a lever ball valve) and a short stub of
pipe vertically and deliver liquid inhibitor into the system. The
liquid is a little less expensive.
You can't really assess it in that way. The limitation of what can
be fed through a length of pipe is ultimately limited by the flow
rate, and the design rule for that is that it should be less than 1.5
metres per second to avoid noise and excessive flow restriction.
The flow will be related to the pipe size and length and therefore you
can say that there is a limit of volume per second for a given case.
This in turn can be related to the required rate of heat transfer, and
you can finally relate that back to the total radiator output fed
through the pipes in question.
Obviously, radiators come in different sizes and can have outputs
ranging from a few hundred watts up to 5-6kW or more.
As a rough rule of thumb, for lengths of up to a few metres you can
say that 15mm tube will handle 6kW. Clearly this works out OK if
you had 3 x 1kW radiators, but won't if they were each 3kW.
is a useful design paper. You can plug your numbers into the tables
and work out exactly what is needed.
I don't know about the Halstead, but most combis will not allow you to drain
down the system and run the boiler, even just for water. If, however, you
meant you cut out the radiator circuit, but the boiler still has pressurised
water in it, you may be OK.
I could imagine that some boilers still require some sort of bypass in the
circuit, but don't know if any do in practice. Internally, the boiler will
probably use the water to circulate between the burner and the internal
plate heat exchanger.
Normally combis do need a pressurized radiator loop of some kind for the HW
to work at all.
So the answer to the OP's 1st question is no. They will be not problem to
try it but it my experience you just won't get any hot water.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.