On Sun, 19 Sep 2004 22:45:15 +0100, Mike Clarke
wrote:



It is a modulating boiler and has an internal bypass so it works OK but
I am conscious of the energy wasted when all the TRVs are shut as the
boiler cuts in from time to time to keep the water circulating inside
itself up to temperature. Since this is an existing system it doesn't
have to be modified to comply with the more recent regs. OTOH I do need
to make some improvements over the current situation where 7 of the 12
radiators have no thermostatic control at all.


Given that situation, there is not a lot that you need to do other
than to fit TRVs on all of the remaining radiators bar one and then
arrange for the thermostat to be in the area of the non-TRV one.




Well, the manual states that demand for DHW will override the CH
requirement and when DHW is no longer required the burner will
extinguish for a waiting period of about 3 minutes before returning to
CH state. I can certainly confirm that the burners always shut down for
a few minutes after drawing hot water.

That's fairly typical behaviour.



[Snip - explanation of room stat operation]

If the boiler flow water exceeds its set temp before the room stat
clicks off then the boiler short cycles. But as you can see from
above this is function of the boiler output, rads etc. You can't
really stop it with controls unless you vary something above (i.e.
increase rad size etc.).

Yes I appreciate that the boiler will cycle in this way when it can't
modulate down low enough. This form of cycling is OK, it's saving
energy. I was more concerned about the wasteful cycling when all the rad
valves are shut and it's just circulating through the bypass. Perhaps
I'm just being paranoid and the total heat wasted will be very low
compared to the heat used in warming the house at other times.

It is very little energy but if you can avoid it it is better to do
so. You will probably find that the boiler adopts a different
on/off pattern at the bottom of its range to avoid rapid cycling.
It knows from how it has controlled the burner that the requirement is
low, and it also knows that this is because there is little or no
demand in the heating circuit.

The room thermostat hookup would eliminate it as long as you set the
temperature of it and the flow in the radiator appropriately.




..andy

To email, substitute .nospam with .gl