"t" wrote in message
...

The CORGI registered man fitting the boiler for us is saying that we must
have a bypass. I know what this is. He says it is due to 'new'
regulations. He does not say whether these are building regulations or
Corgi regulations.

None. Corgi is a registration authority only. You indicate that the
bathroom rad has no thermostat valve on it. If so the by-pass is there. If
it does, say a mechanical one, then a mechanical by-pass between the flow
and return at the boiler may be fitted.

If you have electric thermostat valves on all rads then no by-pass is needed
if the boiler is control "interlocked". That is when all are off the pump
and boiler is off. You may want to put a by-pass in to maintain a minimum
flow through the boiler if only one rad is partially open.

Another way is to have a Grundfoss Alpha auto speed pump and a flow switch
on the reads return. When all rads are closed the flow switch cuts out the
boiler but not pump. No flow and the pumps automatically winds down. when
one opens it winds back up.

He says "safety" and that he cannot
sign it off (presumably Corgi-wise) unless it has a bypass. He is saying
that in theory if every radiator valve failed and shut off, then the
bypass radiator, which would be uncontrolled, would allow the passage of
water for safety reasons. He also says it will save gas. The problem to us
is he is insisting it must be one radiator that remains uncontrolled. This
is anathema to me! An uncontrolled radiator chugging away every time the
system is on for any one or more other radiators.

He is talking balls. The Baxi 133 HE Plus and Potterton Promax have an
integral flow switch and rad valves can be fitted on all rads. What if that
flow switch fails?

Clearly this cannot save gas. I thought that a bypass was to protect the
circulating pump from pumping against nothing in the wildly unlikely event
that all TRVs were closed or faulty.

A Grundfoss Alpha solves that.

Flow switches:
A selection at Hawco http://www.hawco.co.uk, but have a £75 min order. Try
RS: http://www.rswww.com
Farnell http://www.farnell.co.uk)
Also: http://www.axdistribution.com/FluidM...ow_switchs.htm

Flow switches from Farnell:
FS-05 (3A contacts) 3/4" BSP - £16
FS-01 (3A contacts) 22mm compression £31.92. Twice the price for
compression joints.

Data sheets:
http://www.farnell.com/datasheets/28551.pdf

Is there another function of a bypass?

It is there to maintain the minimum flow through the boiler. Some flow
switches have a minimum flow switch-on. Find out min' boiler flow and match
switch to suit. Fit an Alpha pump. If the flow switch is too low a flow
rate for the boiler, then have a tee before and after the flow switch and
by-pass the switch with 15mm pipe, in this pipe have an in-line isolator
valve. This then will raise the minimum flow through the boiler before
switching in the burner. A fix speed pump can be used as it will pump
around the flow switch by-pass, only when flow get to the min boiler level
will the flow switch, switch in and the burner come in.

Could we use a pipe or something automatic (I know there are various
so-called automatic bypasses) instead, rather than a radiator? As we do
not have a radiator in a room with a system thermostat. Our system will
only fire the boiler if one or more stats calls for heat. I take this to
mean it is fully interlocked?

The problem is the minimum flow through the boiler. If one rad is calling
and just about open it may not be enough flow. The flow switch combined
with a Grundfoss Alpha pump will maintain the min flow

Does any regulatory body, e.g. Building Regs or CORGI specify a bypass as
mandatory?

No. Just a control interlcok, which you have, and makers specs of course.

If they ever do, does a system that would not call for heat in the
situation where all TRVs are -shut- require a bypass?

The minimum flow problem again. You could have one thermo rad valve
permanently partially open, to give the min flow if another rad is open. Do
the rad valves have a min/max switching adjustment? If so you are sorted,
and no Alpha pump needed.

Is it true to say the bypass is a safety item or is it to protect the
pump? Or in some way supposed to save energy?

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

Just ask me questions.