Super_Paulie

I can do that. Sorry John, my understanding of flow rates seemingly can't be solved. I'll open up that shield a touch and see what that brings my return down to.

Very interesting, thanks. I've looked to see if I can edit the anti-cycle time on my Baxi, but alas that seems not an option. How could I reduce the bypass flow rate, just via the boiler flow? I am trying out 57° this evening which is giving me that lower return. Like I say, that thing is tiny but so is the room. It's toasty in there though now my flow temperature is up at 57°, actually warms the top floor if I leave the door open.

John, thanks a lot. Ive been trying to get my head around this on my lunch at work but i just cant comprehend it, im just not educated in boiler flows im afraid. Im not sure what numbers to change to "make this better" so my apologies. Your effort is way beyond the call of duty, but im a mere mortal 😆 So it looks like a "low and slow" way of doing business isnt going to work for me due to not having a boiler than can modulate down far enough, but rather a "batch heating" of the floor just when i need it and accept a 15 minute(ish) cycle time, thats no problem as thats what i was doing until a few weeks back. Having this at a 60 degree flow, 45 mixer is ultimately higher than i wanted on both sides but that gives me a cycle time of around 12, lets say 15 minutes. I have it with a very small bypass rad currently and my house IS warm enough but ultimately i am heating a water tank in the loft that is just sitting laughing at me asking for more money. If there is any way i can get this flow rate down without the system cycle or am i just at the limit due to the boiler? I will be getting a bigger rad and snaking the return under the bathroom floor as a makeshift UFH, that wont add a huge amount of volume but it would take more heat away. Ok, so this costs a few quid a day to keep my family warm, im not going to lose any sleep over that. Thanks so much guys, what a great forum this is and has been in my build so far.

Yeah it's dead on 7 lower, the actuators see to that and seemingly work a treat.

That's interesting, thanks for that. So volume is the thing, I could probably increase that with an additional rad say in the hall plumbed in before the 2 ports. But what advantage would I gain from this increased volume, longer cycle time?

Ah, gotcha. Ok so maybe my probe is a better indication rather than what is on screen. I'll have to do that tomorrow as the missus is back in, boiler in loft, manifold ground floor. I've sat looking at the manifold the last 10 minutes and to be honest the needles barely move at all, maybe a degree or do. All flow rates are 2.5, ish, balanced with Salus. Yeah the smart meter was £2.50 so it's not going to be much higher by the time it goes to it's set back at 11, and 30p of that is the standing charge. It'll stay 20+ in here all evening no doubt.

It's always around -10° no matter what I set the flow at it seems. 65 drops to 55. 55 drops to 45 etc. It just drops to whatever temp is in the tank in those 3 minutes. I have absolutely no "off time" except when it's in that anti-cycle mode.

I've likely misunderstood what I've been trying to achieve here. In fact, I'm not even sure what that is at this stage. I guess my tank just creates volume and not a lot else. So tonight I ran a few tests. I locked off both upstairs rads which get a slight reverse circulation I think as they warm slightly when the UF is running. Ive been using a probe on the return under the boiler to read that but instead I'm going off what it shows on screen when it's not firing and that is surely the return temp. I went with: Boiler 60, mixer 45. Bypass rad (tiny thing, shown above) 3/4 open. So it now fires for 9 minutes as it creeps 60+5. Flames out with a 3 minute anti cycle and the return temp drops to 52 at the tank but shows 56 on screen. It then fires back up and repeat, which I guess is a cycle time of 12 minutes. So guys, ultimately what is my goal here, I'm not entirely sure anymore. Keep the boiler firing for as long as possible until it reaches overtemp and flames out? For what it's worth, it's toasty warm in here at 22/23° and it's cost me £2.50.

really appreciate all this help guys, its helping me understand this all a bit better. The numbers give me brain struggles so its very much appreciated. I have re-drawn my system to maybe show a bit more of the reality. Looking at it as you say, 60 (65) down to 50 once the UFH is away is a big old drop for what should just be a bypass. I do get some, what i thought was, reverse circulation in the rads marked Rad1 and Rad2 in the attached image. Would that combined with the bypass rad in the bathroom account for the loss? To test this should i lock off the 2 rads and see if the return temperature increases? As it is my boiler burner is essentially "never off", and is only off when it flames out at the temp +5 for the anticycling time of 3minutes. I kinda expected the return to get so high that the boiler stops the flame but then continues to pump while being fed from the buffer for however long it takes, not just being off for a pre-determined flame off due to anti-cycle. Probably totally miss-read the situation there.

I've got a rad in the bathroom, not sure if it's better to have that thing fully open or throttled back. As soon as you get flame out the pump is still running so I guess it cools quickly to the temperature of the return from the buffer.

I don't have that exact figure at the moment, but setting the flow at 60, and the mixer at 45 it took an age burning while the buffer gets to temp, at least 30 minutes. At that point it goes over the target temp +5 then the flame out (anti cycle?) kicks in for exactly 3 minutes. In that time the flow temp has dropped to match the buffer return temp then it takes another 30 minutes to get it back up again before repeating. So it's pretty much always firing, except for the 3 minutes it isn't. I have the manual if that's what you mean? The figures start from page 14 and I can't find anything on there or the internet about being able to adjust the cycle timer. Baxi 800 Combi Installation and Service Manual.pdf

I did originally. Having the boiler at 45 and my mixer at 38 I'd get a cycle of 49 seconds flame, then 3 minute off. That's my problem really! I now know (from John C above) that I need to have my flow high enough to beat the boiler trip and modulate down. Currently at 60 with my mixer at 45 but that's just my first test. It's all confusing for myself as a mere mortal so far. This makes sense to me. I could potentially just knock the TRVS right down on the majority of the rads and only open the ones that will give me the volume I need, like in the hall for example. The second suggestion is what I was doing previously before I tried the really low 24/7 method.

I've had to call it a night up there, but before I did I set the boiler at 60, the mixer at 45. This takes a while to fill the buffer and the boiler creeps to 65.1 then flames out for 3 minutes, the buffer is at 51 at this point. After the 3 minutes the boiler is now at 54 and it starts up again. Runs back up to 65.1 in around 30 minutes. Is this still short cycling even with the long burn time and then 3 minute flame out? Correct, just on the UFH circuit. Rads are rarely used. I have no means to control that, I wonder if Baxi themselves can advise, I'll email them. House is toasty and not expensive to get it that way. Just the boiler is probably getting upset. It's just on/off, coming from a Heatmiser wiring center. Not sure OpenTherm works with that, I'll have to check online.

Currently I've got my mixer at 45. I've got the boiler at 55. The return temp from the buffer is 41. Flame on takes it to 59 and it messes about a bit up and down at around that, slowly creeps to 60 then it cycles, dropping to around 45 as it does so. Repeat. This feels like a problem I could solve, but I've got redundancy brain... 😕

I previously had it as I guess timed, where the stat has set times and it just reached those set points and pulled the plug, keeping it going on and off to keep that temp. This actually works well but still cycles as it does so. I'm disappointed as I thought the buffer tank would stop that, or at least help extend the times. So having the boiler fire for like a minute then cycle out is sad and seemingly hasn't been worth the effort so far. I just end up with a tank full of hot water. I mean my bills are small(ish) but this is obviously out of control compared to what I had in mind.

Once the target on the boiler goes below its temp setting it fires up, goes over temp and then the short cycle delay kicks in for 3 minutes. I just tried setting my mixer up 45 and my boiler to 35. Buffer is basically hanging at around 34. What happens is the boiler gets to 34.9, fires up to around 45, flames off and then cuts out, cycling for 3 mins then repeat. Can't find anything in relation to gradient, but I'll keep looking. I've closed the bypass rad so it's barely on, hasn't helped sadly.

Thats interesting, i'll google that now. I use Nest 3rd Gen for the stat, ( Nest stat )but when im running it low and slow i set the stat so its basically sat at a cut out temp of 25. It never reaches that so just chugs along and equals out at the temp i want, usually about 21. When im doing the timed heat i set it at what i want, 23 usually. The mixer, im not sure what it is. Might be Reliance but id imagine its a cheap knock off version. It goes down to 38 and seems pretty accurate to that.

the boiler and the tank are in the loft. The tank is jacketed, plus i have it basically encased in a 75mm PIR tomb. The bypass rad is in the bathroom, its tiny but will be replaced on bathroom refurb time. Its operated from the flow and return before the 2 ports so its running through whenever the boiler is running. Buffer

hello friends. Yet another "short cycling" thread sadly that id love some advice on. Not sure if its a) my plumbing b) my electrics or c) my lack of knowledge on it. System My system is a gas combi boiler Baxi 830 (or 800, cant recall) (30kw (or 24kw, id need to check the model), modulation 5:1, way oversized by plumber when i didnt know better), UFH downstairs and rads upstairs, on separate circuits via 2-ports etc. 4 loops, roughly 400m of 16mm, 2 zones (running as 1 zone currently)100/120mm centers in biscuit mix, 170mm PIR, flow rate via Salus auto-balance 2.5l-ish. On the advice of you wonderful gents i also fitted a buffer tank (50l) at the time of install with help from @Nickfromwales and @JohnMo, at the time i didnt have a clue about having to do this, i was uneducated on it (still am to be fair) Buffer tank saga I run the tank plumbed into the return as a 2-port and its only in play when the UFH valve is open. When the rad valve opens the tank is bypassed via a 3-port valve wired into the rad valve, everything's golden. I also run a small nearby bathroom rad as a bypass which runs independently as it is plumbed in before the 2x2-port valves. Ok, so i can run my system at the lowest setting on the mixer of 38 and have it run 24/7 keeping the house a constant 20/21. Or i can run it as a timed system with a mixer at 40/45 to make the house 21 in the morning and then 22 for the evening with a setback of 18. I have tried both ways and the consumption is basically the same, when its very cold outside it costs about a fiver to do this, other times 3 or 4 quid, great (i guess). Short Cycling So, i assumed this was all working correctly, the boiler is in the loft so out of sight, out of mind. I went up there on a whim to time my cycle and found out it was short cycling. What it does is the boiler gets up to its target temp, flames off (pump still running/over-run?) for exactly 3 minutes while the temp drops, then flames on and repeat. It seems to do this no matter what i set the boiler flow to. When it fires up with a cold buffer it takes a good half an hour for the return temp to come up before the above happens, but when warm it cycles as below: UFH mixer Boiler flow Return Flame on Flame off /buffer temp 38 40 (45) 34 0.47 3.00 38 45 (50) 35 1.40 3.00 38 60 (65) 49 4.20 3.00 after i ran it at 60 for a while i then turned the boiler flow down to 40 and it took a good half an hour for the buffer to empty while being pumped around the system by the boiler, satisfying the UFH demand. This i what i thought i was building (what id like to have?), the boiler fills up the buffer over 10 minutes then it takes 30 minutes to empty, and repeat. Obviously it doesnt, the boiler is always trying to satisfy the heat it is set at, duh, its a volume buffer not a storage tank. So my question is, is this running as its meant to? i thought the addition of the buffer was meant to alleviate the short cycling, which it does but only if running from cold so its short lived. Im not sure what i was expecting but as the 3 minute flame off is always exactly 3 minutes thats obviously an anti-short cycling function of the boiler kicking in. I mean its only costing a few quid each day but it cant be good and is obviously a failing somewhere on my behalf. I have attached a simplified diagram below to maybe help explain my system. What have i done wrong guys, do i just need more volume? run the mixer hotter to bring my return down? Unfortunately i am going through a redundancy process (sob story) so my build is on hold so id really like to see what i can about this if anything. Thank you people.

i have those Salus ones and im pretty sure the flashing means they are in calibration mode. Have you recently powered them on and off in quick succession?

probably just keep an eye on it then and repair in the future if necessary. Fully expect it to crack at this point but onwards and upwards!

yeah its an absolute beast, 305x305. What can ya do, the engineers calculations came back with that and i aint gunna argue as we love it and everyone who sees it says how mad it is, a great talking point. Its marked "British Steel", id imagine it sat as surplus from a car park before it ended up in my house. Yeah it needs fire protecting, thats a christmas job. Anyways, so caulking the corners is not something to do? i'll just leave it then and caulk in the future when/if it cracks.

As I'm at the decorating stage, got a question for you guys. I have a hefty steel beam, with a small, maybe 2 inch section of plasterboard and skim above it and then the ceiling. Although this joint is fine currently, I'd imagine the house is still settling and thus the join will likely crack, no doubt as soon as I'm finished decorating. Would it be an advantage to mist coat, then go along the wall/ceiling join with decorators caulk before my final coats of paint? In my mind this will add a flexible joint in that section that will crack if it's just skim. Any opinions?

ive ordered some SBR so i'll go with that. Cheers guys.

You see, that's where I'm at. The internet was all this way or that way, and so far on here I've got the same. To be fair I painted my last wall and when I removed the tiles they came away like they weren't even attached in the first place. Not sure if that's a good or bad thing but I never experienced any issues in their lifetime. Really looking for a definitive answer on this, maybe run a poll?