@jamespa @bami 

Just to clarify, I have already done what James has suggested. My water law settings are as low as I can use.

@jamespa I haven't forgotten 🙂  But I want to talk to the tech chap at the installers before I start altering the system, just so they can't accuse ME of being the reason the system isn't running efficiently.

Apart from putting the DHW on a timer, and altering the low end of the weather comp to -2C from 2C the system is as it was commissioned - for now at any rate.

Posted by: @bami

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@jamespa I haven't forgotten 🙂  But I want to talk to the tech chap at the installers before I start altering the system, just so they can't accuse ME of being the reason the system isn't running efficiently.

Apart from putting the DHW on a timer, and altering the low end of the weather comp to -2C from 2C the system is as it was commissioned - for now at any rate.

No pressure or obligation, this discussion has moved on so much I felt it worth restating in case you had missed it.

Installers will probably say touch nothing, which eventually you may have to ignore, but you are imho right to be cautious while you are trying to get them to change things!

Update for those following this thread.

Finally got the 'tech guy' from the installers to email me.  I sent him the plan the surveyor had done, which was completely wrong, and the plan I've done which is correct.

He is trying to tell me that the plan I was sent was just to show the rad sizes and pipe positions and has nothing to do with the heat loss calculation (which I haven't been sent).

I told him that if the BTU for rad sizes has been calculated off the surveyor plan he sent me, in which the room sizes are incorrect, windows are missing and it shows a heat loss outside wall which doesn't exist, how on earth can the rad sizes be correct.  He's still saying they are - which is nonsense.  For starters, the utility is 6.48 m2 and has a 70cm x 80cm radiator, while BR3 is twice the size at 12.24 m2 but only has a 70 x 50cm radiator.  BR3 is always cold.

I asked if the heat loss calculation was done via a different house floor plan and if so why? No response to that!  I've now asked for the heat loss calc and the house plan that was done off.  Will see if I receive it.

He has arranged to come for a visit this Friday, so I'll report back after that.

I don't want to tamper with too much until he's been, but did check the rad valves in the lounge (which is always chilly) and they were closed by a 4.5 turns!  So I've opened both up to max and the rads are definitely getting warmer in there - thanks for this advice.