I posted back in January looking for (and getting, thanks) advice about
upgrading a very basic CH installation in a new home in Ireland.

I'm now in the process of doing the upgrade and I'd appreciate some
more advice about whether I need a differential bypass valve. The
system is currently the very basic installation described at the start
of the "Valves" section in the FAQ. The boiler (an external WarmFlow
boiler) does not require pump over-run. The system is currently
controlled by a mechanical timer. There is a ball-valve to shut off the
CH zone when no heating is required and a gate valve to shut off the HW
cylinder.

My plan (as per the advice received here), is to install a 2-channel
7-day timeswitch, 2 motorized valves, cylinder stat and room stat, with
S-plan type wiring. At the same time, I will install TRVs on all the
radiators, except for the two radiators in the hall and landing (which
I'm treating as one room) where the room stat will be.

My question is, given that there is no need for a pump overrun, will
the two rads without TRVs be sufficient as a bypass, or do I need an
additional bypass valve in the circuit before the motorized valves?

Cheers,
Jonathan

On Thu, 26 May 2005 04:41:11 -0700, drseafisherman wrote:

I posted back in January looking for (and getting, thanks) advice about
upgrading a very basic CH installation in a new home in Ireland.

I'm now in the process of doing the upgrade and I'd appreciate some
more advice about whether I need a differential bypass valve. The
system is currently the very basic installation described at the start
of the "Valves" section in the FAQ. The boiler (an external WarmFlow
boiler) does not require pump over-run. The system is currently
controlled by a mechanical timer. There is a ball-valve to shut off the
CH zone when no heating is required and a gate valve to shut off the HW
cylinder.

My plan (as per the advice received here), is to install a 2-channel
7-day timeswitch, 2 motorized valves, cylinder stat and room stat, with
S-plan type wiring. At the same time, I will install TRVs on all the
radiators, except for the two radiators in the hall and landing (which
I'm treating as one room) where the room stat will be.

My question is, given that there is no need for a pump overrun, will
the two rads without TRVs be sufficient as a bypass, or do I need an
additional bypass valve in the circuit before the motorized valves?

The answer depends on the boiler if it requires a bypass and/or has pump
over-run it will need a bypass so there is always a circuit for the water.
If it needs neither a bypass nor a pump-overrun (probably means it's got a
cast iron heat exchanger) then you won't need one.
If you do need one then a smart one is the best idea.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html

Cheers Ed. There is no mention of a bypass in the installation manual
and an email from Warmflow has confirmed that no pump over-run is
required. However, I'm considering installing one anyway on the basis
that for =A320, it's better to be safe than sorry. Also, given that's
it's an external boiler, it should have a frost stat and I guess
that'll need a bypass.

Can I ask a potentially stupid question and risk demonstrating my
complete ignorance? Why are differential bypass valves right-angle
joints? Surely in most installations the flow and return run in
parallel at some point and the simplest bypass would be two tee joints
with a straight bypass in between. Feel free to point out if this is
nonsense.

Jonathan

On Thu, 26 May 2005 14:41:31 -0700, Jonathan wrote:

Cheers Ed. There is no mention of a bypass in the installation manual
and an email from Warmflow has confirmed that no pump over-run is
required. However, I'm considering installing one anyway on the basis
that for £20, it's better to be safe than sorry. Also, given that's
it's an external boiler, it should have a frost stat and I guess
that'll need a bypass.

There are several ways a frost stat can be implemented.
1) By boiler, with smart bypass, not dependant on time-switches etc.
2) By boiler, in parallel with the house heating thermostat and timer -
this will heat the whole house when the boiler gets cold but the house
will be protected as well perhaps needlessly so.
3) Using the frost protection feature of the house heating (say 10C) to
protect the boiler (might not come on to protect it).



Can I ask a potentially stupid question and risk demonstrating my
complete ignorance? Why are differential bypass valves right-angle
joints? Surely in most installations the flow and return run in
parallel at some point and the simplest bypass would be two tee joints
with a straight bypass in between. Feel free to point out if this is
nonsense.

Firstly the way they work is not very different to a tap or a rad valve
but with a spring rather than a screw, so although they could be
made in an in-line form the 'natural' design is for as an elbow.
For every place where the 2 Ts would help then there will be somewhere
else it would hinder. Often the installation place is close to the boiler
or cylinder were the F&R pipes are not pipe-clip-distance-separated.
HTH




--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html