Weather Conpensation - heating settings

What is your heating system @BPLightlog ? 

Gas boiler .. 2years old

Interesting... 

Can you adjust the weather compensation curve? 

Is the weather compensation feature also using the internal temperature or just the external temperature? 

Do you have your heating on 24x7?

What flow temperature are you using without the weather compensation? 

Are you confident any radiators are correctly sized and balanced? 

Anything unusual about the piping in your home? 

I can adjust the start and end points but not the curve as such

There is an internal thermostat (smart stat), thermostatic radiator valves and another smart (controllable) stat in a small annexe - all fed from the same system

No - timed with various adjustments during each day. Individual days are individually adjustable

58 deg C but interestingly with the eco setting on, I can see at present it is 41.4 deg C

Yes - adjustments made when boiler was fitted and reviewed at annual service (last done in Jan)

Don’t know if it’s unusual but where we are due to the nature of the type of rocks, there is a requirement to have a void under the ground floor, so some of the pipework uses that void.

It was just that whilst I can see the advantages of external weather compensation, the occasional ‘lukewarm’ nature of the radiators feels odd and the house in general doesn’t feel right (It is just a feeling as the temperature does reach the set point quite well). The house is fairly open plan and so I have spent some time this winter ensuring the draft proofing is good. The house has cavity wall insulation and an insulated loft.

Then i think the issue may be the way the system is setup and running.

Just like a heat pump with weather compensation, you need to think differently. 

For example usually it is better to remove all the thermostats and TRVs and let the weather compensation system run your heating. The TRVs will throttle the flow through the radiators a bit at all times for example. This won't work well with the lower flow temperature at times of the water.

You have basically got multiple systems trying to manage the heating which always causes issues with efficiency. 

The lower flow temperatures at times with weather compensation may mean your radiators are undersized so you may need to experiment with the weather compensation settings. 

Some of the heat pump owners can probably give you some ideas to try and what you might need to think about changing. 

I understood that part L of building regulations made it mandatory for trv’s to be fitted to all radiators except where the thermostat is located. They were fitted as part of the boiler installation 

Weather compensation is simply a way to run the system at the lowest possible flow temperature. If you're getting better efficiency with it off you've got one of a number of issues 

1 - There's another control in your system that's moderating the flow temperature, which is setting lower flow temperatures.

2 - Other controls in your house (e.g. TRVs etc) are interfering with how the house warms, which can impact efficiency.

3 - The efficiency change with a gas boiler will be marginal so the difference might be due to external factors (solar gain, different numbers of people in the house etc).

Some people with Mitsubishi heat pumps have found that weather compensation isn't always the most efficient way to run their systems. Mitsubishi have an alternative optimisation system that uses an internal thermostat as well as the external temperature. It could be that your boiler has built in optimisation that is doing a better job than the weather compensation function.

Yep. But they don’t work well with weather compensation unfortunately.

That is the problem. The regs are designed for the old way of heating and haven't kept up. We have a mess of regulations, some of which are for a different era. 

At the very least open them fully and see if that helps. Just use them in the bedrooms.

TRVs aren't on/off, they gradually turn off, so they are throttling the water at the same time the weather compensation is throttling the water temperature. That isn't a great control as heat pump owners often find who are the more normal users of weather compensation. It is less commonly used for gas boilers so far at least.. 

It will probably take quite a bit of experimenting to find the optimal solution, but there are some common things to watch out for. 

As has been said, this appears to be another subject with not enough known to offer the best advice. After contacting my installer and system manufacturer (the smart stat and boiler are part of the same system) they both suggest that I should be using TRV’s alongside weather compensation. Even in my control system it gives me the following advice: 

I’m still experimenting with running my heat pump. I have weather compensation switched on and the room sensor also sends indoor temp info back to the controller which can modulate the radiator temp up or down, eg when there is solar gain. The radiators are large which means they can give out enough heat to keep the rooms at the target temp. They all have TVRs fully open. I’ve set that to 21 C daytime and 20 C night time, which was a huge stretch to begin with as I really wasn’t used to heating the house at night. In fact it nearly never comes on at night time except when it’s been sub zero. There is no on/off time switch like our old gas heating.

Whether that would be how to run a gas boiler with weather compensation I don’t know, but certainly the heat pump temps are low: eg today at 12 C outside the rads were 32 C, rooms were 21 C. Back in December when it was -1 C outside rads were 45 C.

If your radiators aren’t huge maybe the temp graph needs to give higher values?