@jamespa Thanks so much - so are your bedrooms on a different zone to the rest of the house?

Posted by: @richdorm

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@jamespa Thanks so much - so are your bedrooms on a different zone to the rest of the house?

No the whole house is on one zone operating at a single FT. 

In principle the rads in the bedrooms should have been designed for a lower room temp (ie made smaller than would otherwise be the case) but in fact, for historic reasons, they are oversized.  I just turn down the LSVs in the bedrooms, which has the effect of reducing the flow rate, thus increasing the deltaT, thus reducing the average flow temp in those rads only.  Put another way the rads are balanced for the desired differences in room temp, not balanced for equal deltaT.  Does the job!

Posted by: @richdorm

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@old_scientist so - I have a Hive thermostat, which I've currently got set to 25 (!) so that I could set up the water law without it interfering.
I guess having the hive means I've got an "external thermostat" then?

So once I've set up my water law (which I've more or less done) then I could schedule the hive to be (say) 2C cooler at night than the desired 19C - which would have the effect of limiting the pump.  Is this correct?  Most people say "don't use a hive!"

I'm not familiar with Hive thermostats/controllers, but as @jamespa says, not all external thermostats work well with heat pumps. Mine has 3 different modes, so I just use the simple on/off configuration rather than one of the clever modes designed to work with boilers.

Again, as @jamespa says, you have two choices - you can either set a lower room temp (say 18C) which will switch off the heat pump until the house cools and calls for heat again. Or you can manually adjust the flow temperature (as set by WL) by +/- 5C on the front screen of the Samsung controller. Once you have your WL correctly set up, you could try setting this to -2C overnight (before bed) and turning it back to 0C when you get up. Unfortunately there is no easy way to schedule this, and finding the correct offset may take a few attempts. Manually setting the flow temperature to run 2C cooler (or whatever value works for you) should allow the house to cool a little overnight.

I have an EPH CP4 programmable wireless thermostat (recommended if you want a 3rd party thermostat that is convenient to use and ASHP compatible) which allows times and temperatures to be programmed which works great for the first approach as we're not really able to use the second approach as my heat pump puts out too much heat for my property overnight, even when the flow temps are turned right back to minimum, so the thermostat hard on/off is the only real option for us (with an oversized heat pump) to maintain an 18C overnight temperature. If you can achieve the desired set back by manually reducing the flow temp overnight, then that becomes an option for you.