@andrewj very similar to my experience, just set and forget 👍

@andrewj i've been keenly following your journey since you first described your problem / aims and I have learned so much both from your experiences and from the responses you have generated.

I sense that you have reached a position now whereby any further gains are not worth the effort so well done.

Drawing upon your experiences (and the advice gained from browsing other threads and videos on this hub) I have adjusted, tweeked, asked stupid questions, tweeked again, etc., and I too now feel that I have got my system in a reasonably good state.

I have had doubts about the Cosy ashp along the way but am now a bit more at peace with it. I'll continue to monitor it's performance daily until I have had it a full year and then I'll see whether I can draw any more conclusions. One key lesson has been not to fiddle too often, to allow a few days before the next tweek. 

Kev

@kevh certainly I would not choose a Cosy again because it doesn't allow a low enough flow temp, doesn't give enough data points to help sort out balancing and running problems, and it can be quite noisy when running hard. I think my problems stem from an over estimated heat loss survey installing too large radiators  which ought not to be a problem but see the issue with flow temp. I suppose the flow temp issue wouldn't be one if radiators were right-sized.  Octopus did come and do another survey and determined that heat loss was actually 1000W less than first estimated; the updated radiator schedule allowed for 1000W MORE output with only 6 radiator changes, 4 which were smaller and 2 which were larger (as explained above.)  Despite asking if anyone had sanity checked it, I received no response. To be fair to them on this point, I had suggested we just replace the two and then I work with one of their technical team to resolve the other issues (didn't happen.) 

Anyway, apart from the bedroom which is too warm, once that is sorted out, I too will be more at peace with it.  And the main thing is, the wife is very happy with the temps.

Posted by: @andrewj

↑

@kevh And the main thing is, the wife is very happy with the temps.

I guess at the end of the day, this is the main point.  Warm house + reasonable cost = happy wife

I too wish that there was more scope for user intervention, particularly around flow temps at low OAT, and I can't believe that Octopus are now pushing a 60c plus FT variant.  Yet people are installing them...

My main concern is the Cosy tariff; how will it evolve over time?  I am guessing that it may morph away from a TOU tariff to one that only discounts heat pump usage, with all other usage being more expensive.  

I have my first service next month and hope to glean a little info about what the new PCB is for. 

@andrewj Your final sentence says all that needs to be uttered of course!😉

Providing that space in the rooms has not become acute as a result, oversize is better than undersized emitters as there is the potential to manipulate the flow on those that are still providing too much heat. Very small ‘entweakments’ (just invented that word but it seems to say what I meant😉) of the LSV’s in those rooms may enable you to tame them, adjustments measured in mini-nadgers may be required of course. Regards, Toodles.

@kevh Manipulating a TOU tariff such as Cosy sounds counterproductive to me; after all, the whole idea is to even out the times of lowest demand and decrease the highest demand points at other times. Spread evenly over the 24 hours, I gather we have sufficiency in the present grid structure to cope very nicely thank you. (That is correct isn’t it @transparent?) Certainly with battery storage use, TOU tariffs should go a long way towards making this possible. Without TOU ‘encouragement’ we will continue to have high demand times for the consumers convenience and all the problems that brings. Regards, Toodles. (Sorry for thread shift!)

@toodles the LSV in the bedroom is only just cracked open and I will see how it goes.  For most of the day, the room has been sat at 23.2c, up from 22.8c when I opened up the TRV and turned down the LSV!

@andrewj If a milli-nadger adjustment is just not possible, maybe this is one of those occasions where the TRV just has to be employed as a limiter then! (Only a suggestion, I would still try to explore the LSV adjustment if possible, the ‘control range’ of some LSV’s is in the last 1/8 of a turn or less!) Regards and Good Luck, Toodles.

@toodles if @andrewj needs to turn the lock valve to almost shut, doesn’t that point to the radiator being way over sized?

The diameter of the flow pipe is the limit on the heat flow/hour into the radiator. I resized all my flow/return pipes to the radiators from 10mm to 15mm as I wanted a quicker response to heat the rooms, only 1 bedroom is still to slow to respond and ill be increasing the radiator size during the summer.

regarding flow temperature, what’s wrong with the cosy FT at 37C. I’ve tried mine at 30C, the lowest it'll go, and the downstairs UFH slab couldn't keep up with the drop in OT in the evening. Maybe it’s different if you have radiators in stead of UFH; has anyone else experienced low flow temperature with an UFH slab?

@agentgeorge they are oversized, except now the porch and downstairs wc which are now about right.  According to the radiator schedule the kitchen is 333% of requirement and the study/office is 240%!  I don’t trust their heat loss calcs: as mentioned above it just seemed incorrect given the 1kW improvement in heat loss but 1kW increase in heat output from rads.  

The bedroom luv is now open a “nudge” and the temp is slowly coming down: at 22.8c now.

@andrewj loads of factors can throw it out, I mean air changes can make a huge difference aswell. Also, hardly any models do solar gains. Inside the thermal envelope it should all even out anyway - just varying how efficiently that's happening.

@swwils I’m not too worried about things like solar gain as it’s a bit out of anyone’s control.  In fact the porch now gets over 21c on sunny days because of solar gain but not for long as it is north facing.  I still think that on the basis of 9000kW of gas heating in 2024, the Cosy 9 is oversized but I don’t have access to any data to check.  I only need to sort out the bedroom now and everywhere else is good.  It’s a shame that Octopus:

• don’t /won’t share their heat loss workings nor take account of previous recorded gas usage for heating;
• have a heat pump that is controlled by software that limits the WC curve;
• provide no access to operational data (that they have access to) except input/output power for an hour and average OAT over that hour;
• Commission for, and highly encourage, running under thermostatic control.  It just isn’t appropriate to heat a (most) house based on one room’s heat loss;
• runs a bit noisy when it’s cold (<3c to 4c).  This seems to be hit and miss with people and some are really affected by low level frequency noise.  Statistically, there’s not enough evidence to say it’s a problem.  Certainly I find it noisy if I’m awake BUT it doesn’t wake me up nor does it necessarily stop me falling asleep but it can add to other things that mean I end up getting up for a while.

Their service, in my experience, is excellent.  Installation is professional and well conducted. The cost is competitive - in my case £12,000 cheaper than Heat Geek after BUS grant.

I’m glad I have a nerdy gene in my body to investigate and work through problems.  These things definitely require more proactive aftercare from installers for the majority of people.