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I think I covered this already, that sensor (reported as 'Wiser Heating Channel 1' for me) is on all the time (except during a short window after the temp exceeded set point due to cooking). On the graph in the post out quoted that sensor is shown just above where I snipped the screenshot. A few days ago I limited the boiler max temp to 50C and during that time it wasn't enough to heat the flat so the wiser heating demand was above steady state. In that condition, the boiler attempted to heat and cycled according to the limitations of my CH systems ability to transmit heat and the minimum modulation of the boiler. That cycling was very orderly with consistent on/off times and about 6.5 cycles per hour. Since then, I've upped the boiler max temp which has allowed wiser to reach setpoint ang obtain tight control (varying the boiler setpoint via opentherm). However, this seems to have lead to a significant increase in cycling, especially very short ones as explained above. Fundamentally, I think the cause is that my CH system is badly sized and can't handle steady temp running. But equally, Wiser could likely be designed to handle this sort of system more gracefully.

Somewhat, it's down the the interaction between the boiler and how it meets the opentherm setpoint (which is set by Wiser and changed constantly). When Wisers 'Heating Demand' measure started oscillating so did the boiler. I changed the set point then to force a long continuous burn and after I dropped the set point again we are now back to no oscillation and less cycling. Now I imagine there could easily be a feedback loop where the boiler cutting out due to insufficient modulation for my CH system triggers the oscillation. My comment earlier was that wiser doesn't offer a way to rate limit or filter this setting which makes cycling more likely. Opentherm also offers a way of turning the flame on and off remotely without using the relay. I don't know if wiser is using that ability or not. This is all somewhat off-topic for this thread though. I want to optimise what I have to the best extent possible physically, then explore wiser more. My plan is: 1. Complete tweaking balance, etc 2. See how wiser works if asked to just manage the temp in the warm part of the home. (it should be able to satisfy that with lower temps and the colder unregulated rooms will act as a bigger heatsink to prevent cycling). 3. See what difference these fan kits I've ordered make (GPT suggests they could double the heat output of the radiators at high flow temps but don't help that much at low flow temps). 4. By the time I've done this I will have had more time to think about radiators. Looks like I can replace the two vastly undersized ones for ones with 2.5x the output for about £150 if I don't mind sacrificing matching the existing. I can't justify the cost of matching existing but moving to the cheap ones might get payback (and if I keep the old ones I can always swap them back in if the new ones cause issues with buyers/valuation). 5. If I do upgrade radiators then I go through the above again 6. If still having problems talk to wiser Good news so far is that if I've done my sums right my gas usage is only about 50% more than normal heating the whole place vs what I was doing before. Given the heating is on for >14 hours a day vs maybe 6 before this doesn't seem to bad (more than I'd like long term though). This means I'm not in a huge rush to finalise this process and can take the time to try things out

Yeh that's basically been on all day.

By the CH light do you mean the flame icon? I don't tend to look at the thermostat but rather the app, but it has a representation of the same. It doesn't appear to be directly connected to the opentherm requests. I've seen plenty of times when the boiler is active (and cycling) when the flame icon is off. I initially thought it was a bug (and my boiler was ignoring opentherm requests) but after a decent amount of observation I think the flame icon represents not matching the setpoint. ie, in a traditional on/off system, when the thermostat calls for heat. But with Opentherm it's trying to modulate the flow to maintain the set point to a much more precise degree (within 0.1C) and as long as it considers itself as successfully regulating that then the flame is off. The relay signal to the boiler has stayed on all day barring once around dinner time when cooking pushed the temp a fair bit above set point at which point the relay switched off. What I think is happening in my case is that Wiser adjusts the setpoint it wants from the boiler constantly based on the heating demand % supplied by the thermostat. Wiser wants the boiler on all the time to maintain the set point. The boiler is willing to exceed the set point by a certain amount but if it goes over that then it shuts off. I think there's more to it than this but feels like the main issue. I assume you mean since you moved to weather comp and not using opentherm at all. That's not really something I want to do (given the amount of disruption running the cable would involve) and I'm not sure weather compensation would help when the CH system can't dump out the heat from the boiler at minimum modulation.

3C (seems to track the difference measuring at the pipes closely) I did have it at 8 or so yesterday with the lockshield about a quarter turn open

Since yesterday, I've opened up various valves, the two most distant radiators fully open, and opened the towel rails a bit. The system manages very long burns if allowed a higher temperature and it's not close to set point, but as it gets close to set point it drops the temperature and cycles more. By staring at the Home Assistant graphs, I'm still seeing some very short cycles but a lot of them I can connect to Wiser demand changing mid flow (which seems like a bad design from them). BTW I do have it set up as Oil boiler, which should limit things to 3 cycles per hour, but obviously getting a lot more than that.

Measuring the pipes before the valves. I started with a thermal probe (admittedly designed for meat). Wasn't convinced I was getting accurate temps (I think I could do but it was frustrating and fiddly). So I bought a IR thermometer. After a bit of learning how to get good results from it (keep distance short, make sure sensor is in line with what you want to measure, black tape over exposed copper, etc) I think I'm getting good readings. They are broadly similar to those with the meat probes (good thing about them is they could measure both at same time). I am also reading the boiler flow/return temps via Opentherm using the Home Assistant Wiser integration, though these temps are not quite the same as those measured with the probes, the deltas are similar. All BBOE

Sir, this thread is talking about connecting up a man-cave The EV-Ultra cable was suggested as an easy way to do it.

Making compensation fair (or even generous) would seem like it might make things go more smoothly.

Sorry, Retractive. https://www.screwfix.com/c/electrical-lighting/switches/cat7320002?switchproducttype=retractive

Wire the shelly to a retractable switch and program it to boost for 1 hour if the switch is pressed.

Sorry, I actually misunderstood the features of that device. I was thinking of something that had a built in timer (that wasn't adjustable by the guest) with a boost button that they could press for extra heat.

Finding GPT really useful for this. It suggests: 2K water temp drop, combined flow rate 26.9 L/min 5K water temp drop, combined flow rate 10.2 L/min 10K water temp drop, combined flow rate 4.65 L/min I guessed at some of the heat loss specs but they are roughly inline with what I've seen while browsing radiators. So in summary, to ensure sufficient flow I need to balance to maybe a dT of 2-2.5C? (I doubt my boiler will ever fire at full modulation for long at all given the size of the radiators so maybe could target minimum flow and around 4K drop)?

Best it can do is set the pump at 70%.

2x Single Flat Panel 800x500 2x Single Flat Panel 1000x600 1x Single Flat Panel 800x600 1x Double Flat Panel 800x600 1x Single Flat Panel 400x500 2x Towel Rail 500x750 Total 9 All fed via what looks like Speedfit 15mm pipes homerun to manifolds at the boiler. 22mm copper at boiler. Edit additional info: Pipe is through the floor (presume embedded in screed, though can't feel heat through floor except in very limited area near manifolds. Furthest radiator is about 6m straight line away, closest <2m

Two reasons: 1. It wasn't installed as one and I don't have the kit it was supplied with (manual says it should have been included in the box) 2. While I'm sure I could get the kit, the boiler is installed in the centre of the property and installing an outside sensor would involve making lots of holes in plasterboard. As I needed to replace the timer anyway, my plan was to use load compensation instead of weather compensation. It might not be as good but it's a lot easier to set up. Neither is going to be particularly useful with the size of radiators I have in the room with the highest heat loss and the overall ability of the installed radiators to dissapate the boiler output at minimum modulation (6kw) Overall I think so (just wrote a lot on this) but then realise that I think you are just referring to this specific bit: Firstly, there is a bypass installed. I have two towel radiators with manual flow valves only (not lockshields, so nothing to prevent anyone adjusting them). It's not entirely clear to me what they mean by uninterrupted flow. I've adjusted the valves so there is a dT across these two radiators of about 5C. One of these radiators is the closest to the boiler (<2m) so was bypassing a large portion of the flow until I started balancing. 10% of the minimum output of my boiler is 600W. The radiators are 500x750 and looking at similar online they I'm finding outputs specified as ~250W per at dT 50. I struggle to believe that's right given the heat output I get from these (the one closest to the boiler seems to overwhelm the other radiators nearby (assuming doors are left open) putting out enough heat that the other radiators barely come on. Even if these two towel radiators are turned down too much right now, there will still be plenty of flow elsewhere to satisfy the minimum specified above as I have the TRVs removed from 4 radiators with a total output (at dT 50) of approx 3500W, these rads were (at the start of this thread) controlled to a dT of about 8 but all still putting out decent heat.

Good idea! This is what GPT came up with (which seems good to my non-mathsy eyes): Flow rate for the specified radiator and temperatures Given your inputs, we can estimate the radiator’s actual heat output at 60°C/50°C water and 21°C room air, then use an energy balance to get the flow rate. Given data Radiator rating: 550 W at ΔT50 (mean water to air) Inlet water: 60°C Outlet water: 50°C Room air: 21°C Radiator output at actual conditions Mean water temperature: Tm = 60+502 = 55∘C Temperature difference to air: ΔTair = 55−21 = 34∘C Output correction (ΔT method): Radiator output scales approximately as Q=Q50(ΔTair/50)^n. For typical steel panel radiators, n≈1.3. Q ≈ 550×(3450)^1.3 ≈ 550×0.606 ≈ 333 W Flow rate calculation Water-side temperature drop: ΔTwater = 60−50 = 10∘C Mass flow (energy balance): m˙ = Qcp⋅ΔTwater ≈ 333 W / (4180 J/(kg\cdotK)⋅10 K) ≈ 0.0080 kg/s Volumetric flow (water, ρ≈1000 kg/m3): V˙ ≈ 0.00801000 m3/s = 8.0×10−6 m3/s ≈ 0.48 L/min ≈ 28.7 L/h Notes and sensitivity Exponent sensitivity: If the radiator type uses a different exponent (e.g., n= 1.2 to 1.51.5), the output—and thus flow—varies modestly. Across n = 1.2–1.51.5, the flow would be roughly 0.44–0.53 L/min. Fluid properties: If you’re using glycol mix, adjust cp and ρ\rho accordingly; glycol will increase the required mass flow slightly. Direct answer: About 0.48 L/min (≈29 L/h) for water under these conditions. If you know the exact radiator type, I can refine the exponent and give a tighter figure.

Similar here, though pretty sure imperial measures was touched on, though I couldn't convert metric/imperial in my head until much more recently. Whatever happened in school I think I've ended up using Imperial more as I got older* though not for anything important. I've always measured my height and weight in imperial but if I'm measuring or weighing anything else it will be in metric. * In recent years I've been watching a lot of makers on Youtube and a lot of them are American and so I've been a lot more exposed to Imperial measurements than I was when I was younger.

Keep it simple and use something like this? https://www.tlc-direct.co.uk/Products/SMTGBD4.html * Confirm with electricitian this is suitable

I see people say we are crowded alot. I don't think that really stands up. According to the quick check I just did we are the 51st most crowded country. Plenty of far more crowded countries (democracies) exist and don't have the same issues with planning, etc, that we do. Of course people should have their say, but individuals (or small campaigns) shouldn't be able to block things so easily. Wholesale re-evaluation of what parts of Britain we want to preserve with minimal changes and what parts we don't. We need to free up a lot of land/loosen a lot of restrictions at the same time if we are going to solve our issues. The south is so protected, you move from greenbelt, to area of outstanding beauty, to area of special scientific interest, etc, so virtually nowhere is available to build on without huge numbers of hoops to jump through and all these protections just devalue the point of protection. If everywhere is protected then nothing is really special. It's obviously huge difficult to do and I doubt anyone has the political will to do it. The alternative to me seems like slow decline. Old people will die off and not be replaced so we will naturally over the next decades free up some land. But the economic and social consequences of doing it that way are dire.

Agree, it's why I started this thread, to check I hadn't misunderstood something. If I open up the lockshields on the cold room rads again, dT will on those rads will drop to 2-3C, overall dT 5-6C. So just wondering if you/anyone has any suggestions for how to find a middle ground, ie, keeping the boiler happy while maximising dT. I don't think I have any way of measuring the flow rate.

Yeh I agree. Unfortunately, they are not bog standard ones and colour matched to the interior so getting replacements that match the rest is not cheap. I've ordered some cheap Chinese fan kits to attach to the small rads to see if that buys me enough output but they won't be here for a while. If I'd known what I know now a few years ago I would have replaced the rads but given I want to move I doubt I'll be here long enough to get any sort of payback on the rads. Or at least, reverting to my previous heating strategy of ignoring the temp in that room seems like a better plan to me. The other rooms are fine and radiators seem adequate. Maybe not enough for low temp at -5 OAT but should be good at 0. Keston System S30 (A rebranded Ideal Logic with extra gubbins to support 50mm flues). Pump is built in Grundfoss UPM3 15-75 (according to the photo in the manual), boiler modulates pump between 70 + 100%.

It's looking like I can't maintain room temp at OAT 5C unless I allow flow temps >60C. With a DT of 5 that means operation will be entirely non-condensing, unless i've misunderstood something. As I understand it, if I can get my flow temps below 50C then DT doesn't matter anywhere near as much.

Yeh, that matches my thoughts. Any suggestions for the best strategy to achieve this while maintaining as high a DT as possible?

One part of government not co-ordinating with another (planning). So the upgrades were planned then got slammed into planning issues. Supposedly a lot of new build and upgrades to the network will happen over the next 5 years. Paid for out of bills of course, but if it stops curtailment and the associated cost the impact will be more limited.