marshian

No I mean the CH light on the Hub - flame on the app is just saying room is not at target temp - flame out says at target temp

Assuming here you have Wiser Hub and One room stat (no smart TRV's) Watch the hub - if the CH light goes out it's killing the boiler because it's trying to stop temperature overshoot I agree this is an annoying characteristic If the CH light is not going out then it's not interveening My solution to the issue was to set the room stat or a smart TRV to a higher target temp that cannot be achieved - that way the Wiser Hub doesn't get to screw around making the boiler cycle or stopping it mid burn (which is what it did with my old boiler when I had it set up with a really long anticycle timer to give the rads chance to dump the heat)

Whats the delta like if you measure top left corner and bottom right corner of that rad?

How are you measuring your rad flow and return temps? Have you a picture of the rads (as an example) - even my old 1980's single panel, single convector rads at 60 deg C with the old boiler had a half decent temp drop Are they piped up BBOE or TBOE?

Looking at the installation manual it needs 21.5 Litres/Min at Max output pretty much in line with my ball park numbers. I'm guessing as the boiler has control of the pump it's not possible to slow the flow rate down and with 9 smallish rads it's going to have a narrow DT unless the boiler sees that and slows the pump down as well as modulating down to min.

Do that for all the rads and then sum up the total flow rate and you'll have a better idea of the total flow rate. Rule of thumb I've used over the years is for every kW of boiler output (up to 15kW) you need a min of 1 litre/min for each kW to keep the boiler happy (this is probably out of date for modern boilers with good turndown ratio's.) After 15 kW provided the boiler modulates down you can get away with an extra 1 litre/min for every 2 additional kW increase Example - current boiler is 16kW but range rated down to min - most it hits on start up is 58% of max output so 60% of 16 is 9.6 kW Current Flow rate is 0.6 m3/hr = 10 litres / min is more than enough to keep the boiler happy under start up conditions and in normal running Manual Says 633 Litres per hour is the expectation which is 10.5 litres/min

I think you can "back calculate" flow rate thro each rad if you know the flow temp and return temp??

Looks to me like the only way to widen the DT at the boiler and the rads is increase the size of the rads What boiler is it and what pump (If not in the boiler)

Your home is losing heat at OAT 5C - if you need flow temps of 60 deg C to maintain it at target temp then you don't really have a choice Well you do - have a colder house and get condensing efficiency - great or probably not 🙂 Boiler flow rate is really bloody crucial - read the installation manual it should tell you what it's min flow rate needs to be for it to be happy Screwing the flow rate down thro the rads and ending up with a really unhappy boiler isn't a great way to minimise energy usage MWT in the rads is where you need to look Hypothetical Example Rad Flow 60 Return 50 Mean water temp 55 but this is achieved at a flow rate of 104 l/hr and the heat output is 1214W Same rad Flow 62,5 Return 52.5 Mean Water temp still 55 but flow rate would be 114 l/hr Multiply that round all the rads and you quickly add all the increases of flow to make the boiler happier - it stops doing the overheat short cycle and just does equal burns every cycle

Why do you want a high DT?

My advice is simple Keeping the boiler happy with a decent flow rate thro it is far more important than squeezing the DT out of individual rads to drop the return temp Squeeze too much out of the rads and you drop the flow rate thro the boiler Drop the flow rate thro the boiler and it'll go out on temperature much faster Every time the boiler fires you'll send a load of energy out the flue before it modulates down this is a bigger waste than running with a narrower delta at the boiler with a good flow rate

Bingo - so the heat is going somewhere So if the boiler is firing and running for a short period of time you aren't going to get warm water back to the boiler very quickly the rads will take that without giving a higher return temp If the boiler hits temp limit and shuts down then it's going to send "unheated" water round the circuit What does surprise me is that the boiler doesn't shut down because the flow temp exceeds the return by a large margin - many boilers don't like to see difference between flow and return that exceeds 20 deg after a certain period of running. Good example of this was my my old glow worm that faulted out if flow and return went above 20 deg after 5 mins - I had to run the downstairs toilet rad at a high flow to feed back return water to the boiler - the room quickly warmed up and the TRV shut down but by that time the boiler was getting a warmed return from all the other rads

Resulting in a lot hotter water returning to the boiler if the bypass has opened due to system pressure being higher than the bypass is set to Either way until we get some "firmer" temps it's probably not much point. It looks like the boiler running just UFH is cycling a lot more than is desirable - chucking heat out the flue on every start and nit running long enough to stabilise

I get above but if the boiler is throwing out 60 deg C I find it really hard to understand a return temp of 15 deg - in fact I'd struggle with a return less than 40 if the UFH is only taking a little heat out of the circuit via a mixer unit. Unless there is heat being removed elsewhere??

That doesn't seem right - no circulation pump is going to like being almost dead headed What confuses is me is why it appears the return temp is so low - Avg human skin temp is 33 to 36 deg C so anything cooler than that is going to feel colder. I can only "just" feel the difference between my 30 deg flow and 24 deg return on my rads but they both feel cool.

And here

Some discussion here

No - it's pressed up against the underside of the chipboard floor - I had to re-do a bit of plumbing recently - so removed one section - no signs of any mold. I have 3 ground floor surfaces in the house Kitchen and Utility - 18mm Chipboard - 6mm Ply over boarding, Ceramic Tiles Front Hall, Hallway, Toilet and Dining Room - 18mm Chipboard - 18mm Oak Lounge - 18mm Chipboard - 6mm Ply over boarding and 20mm Oak

I've now removed all the "smart" TRV's from the rads and replaced with std Danfoss ones but they are all currently set to max as now we are in winter with a low sun I don't really get any solar gain on the south side of the house anyway. Hopefully I can recover a little back by selling them on a well know auction site. The schedule for heating is 24/7 (no setbacks) In fitting the Danfoss RAS-B2 TRV bodies I've got flow control over all the rads even the ones that needed TRV control to limit the temps Pump is on CP2 - rock steady at 16w 3.1 m head and 0.5 m3/hr System noise is absent and I've been able to make a small tweak to the WC curve (slope and level) now running a slope of 0.6 and a level of -2.0 So 20 at 20 Deg OAT 25 at 10 Deg OAT 31 at 0 Deg OAT 37 at -10 Deg OAT The niggle with the boiler remains but I've removed the range rating and I'm letting the boiler do what it wants.

I did the insulation install across spring and summer - the RH levels spiked as a result of occupants - the "uncontrolled" ventilation had been very effective in managing RH levels (At a cost in the heating seasons) If I turn the PIV off for a few days I pretty much see a steady increase in humidity over that period It costs very little to run (it is run on a schedule not 24/7) Real clue to the uncontrolled ventilation was in the carpet edges - cream carpet was black for an inch at the skirting edge...............

I've got a similar suspended timber floor with a 2 to 3 ft crawl space under it The void is ventilated with an air brick every 5 bricks so has a lot of air movement in winter I've insulated between the Joists with 75mm PIR held up with blocks screwed to the joists (I know it looks like I could have used thicker but the picture below was the extending part of the house with much deeper joists - the rest of the house they are just 5 inch joists It is without a doubt one of the best things I have done to improve the house However as a DIY task it sucked and took me several months to get this Cut to individual size (none of the joists are the same spacing or even parallel) and then moved to under the floor via 2 strategic hatches to limit the level of crawling around. Absolutely awful job but the results have been brilliant. I did have to install a PIV unit to take care of the ventilation strategy as a result of the insulation and drop in drafts the humidity level in the house sky rocketted but the PIV got it quickly under control.

I think manufacturers controls will always be better than 3rd party ones I went down the Wiser route because the manufacturers controls on my old boiler wouldn't have helped - it was already massively oversized and I went down the route of overzoning (but learnt a little on the way) Good to hear - must be a nice feeling. My current nice feelings are driven by last week I had 13 "Smart" TRV's on rads - This week I'm down to 5 - replaced with "dumb" TRV's set as temp limiters but not actually intervening at all the flow temps, room temps and circulation pump output are lovely and stable I expect to completely remove all "Smart" TRV's by next week. (They are just remote room temp monitors now they aren't even attached to any rads!!!! ) I'll end up with one room stat and a hub running a schedule that is 0600 - 0600 ON. I'm kinda loving the simplicity of it

No probs with trying to help Actually systems aren't very complicated at all - it's just warmer water in pipes or rads providing an increase to room temps (or maintaining the temps) One of the reasons I changed my boiler before it had reached end of life is I'm 4 - 5 years away from retirement - Need to ensure I minimise "extraordinary" expenditure when my income drops significantly so I'm very much in the camp of invest now to reduce risk of large capital items hitting me when I'm retired. Electric fan heater?? There is a lot to be said for a boiler in a kitchen even if it does rob a cupboard space (much to Mrs Aliens annoyance)

Similar in my case - data is the key - once you have data you can make better decisions or changes to the system Few years back I was using 16,500 kWh of gas to heat my house on a schedule it was never just right it was too hot or too cold and I was using manual weather compensation (ie i changed the boiler flow temp) - the 24kW boiler was massively oversized for a 6 kW heat loss with a 10 kW minimum and it cycled like a B1tch in the shoulder seasons and not that much better in a really cold snap. Then we had the shock of gas prices rising rapidly and I knew I needed to both improve the house and manage the energy costs. Got it down to 8,500 in the end (CH and HW) but now I'm at 9,500 heating 24/7 with a much more suitable boiler - it's 16 kW with a min of 4 kW and is set up with weather compensated flow temps - house is always comfortable in every room - rads are sized to room heat loss and flow temp is managed by the outside temp sensor - the whole system runs low and slow - it so much nicer to be in the house. Not a heating engineer just someone who wanted to improve/optimise what I had I've not totally finished but I'm pretty damn close..................

last weekend I reconfigured my plant room (aka airing cupboard) because the gas engineer that modified the existing plumbing to suit the new boiler made a horlicks of it - yes it worked but it had way too many joints where existing pipework was used and new was spliced in. It just looked butt ugly and wasn't exactly easy to lag in the old configuration It's still not great but to my eyes it's neater Oh and I don't like leaving bottle vents open and they were on short pipes so I've raised them to add a little capacity with the pipes below them - probably pointless but in my head it works