"chunkyoldcortina" wrote in message
...
Jonathan wrote:
My builder is installing a combi boiler hot water/ heating system in a
holiday flat that we are planning to let out. He does not appear to be
fitting a room thermostat or any sort of timer. Is this normal for
such a system?

I can understand not having a room thermostat as all radiators (except
one) have TRVs but the lack of a timer concerns me. I don't want
enormous bills because the heating is on 24 hours a day.

Can anyone please advise me on what is normal?

It's not ideal but it should work i guess.

All the radiators should be able to have TRV's as Combi systems normally
have an internal bypass circuit.

You need a "control interlock", by law. That means a way of cutting out the
boiler when no heat is needed in the house. This is normally done by having
a room stat with no TRV on the rad. Having the boiler open up a by-pass and
cycle on itself is very inefficient and can lead to premature boiler
failure.

The stat can be a timer/stat, so timing solved. A combi cannot have TRVs
all around, unless there is an integral flow switch. Some Baxi models have
this feature, like the HE 133.

One way around not having an integral flow switch is install an auto
modulating Smart pump on the return pipe to the combi and flow switch just
after that. Wire the combis stat circuit through the flow switch. This
means you have two pumps in push me pull you configuration. If the combis
integral pump is on the return put the smart pump on the flow.

When the TRVs all close up the flow switch switches out the combi's pump and
burner and the Smart pump winds down. When the TRVs open up the Smart pump
winds up and switches in the flow switch which switches in the combi burner
and pump. No central stat then and TRVs all around. You use two pumps, so
it may be a good idea to put in a restrictor balancing valve on the CH
return to restrict the flow of the two pumps. Then the Smart pump will wind
down and not use a large amount of electrical energy.