marshian

What are your L2 settings? I would have thought it was pretty important to have the correct parameters??

Seen that before - my take away is that above 60 mins cycle time there is no efficency degradation - anything below that there is and the shorter the cycle the greater the eff loss

Well for the last three days the boiler has been a very naughty little pixie (Note - It is not range rated at all) Despite falling outside temps the cycles per day have steadily increased - the cycle lengths have shortened Date - No' Cycles - Avg Cycle Length 23/12 - 27 - 21.9 mins 24/12 - 32 - 34 mins 25/12 - 34 - 22.7 mins Boiler behaviour is basically intitial purge and burn up to 58% and then modulate down to 10.8% - it'll sit there for a while before starting to ramp up to 25 -35% even tho the flow temp is already at the WC setting - it'll hit temps of 4 or 5 deg higher than the target temp before shutting down - the return temp would then drive a restart 10 mins later. Once the boiler gets into this spiral of increased cycles with shorter burns it's always defeated my efforts to get it back in line but I don't always have the time to try different things. Normally it goes away with a sudden change in outside temps - either a warmer day or a cooler day. Yesterday I took the boiler off weather compensation mode and set it to a fixed temp setting - boiler did the same thing, I range rated it to minimum - boiler ignored the RR'ing and continued to randomly ramp up. I've powered the boiler down - several times - made no difference I set it back to Weather Compensated flow temps - still the same In the end I turned the whole system off for an hour and then restarted it late yesterday evening. Overnight normal behavior is resumed...... It hasn't missed a beat all day As of 16:30 today Date - No' Cycles - Avg Cycle Length 26/12 - 15 - 40 mins Should end the day at 22 or 23 cycles (one of those would have been HW) Which is exactly as it should be. So I think it's time to schedule some stops into it's activities as opposed to an overnight setback temp My Wiser controller isn't currently linked to the boiler (it has a link wire providing power to both perm live and switched live but a single core cable from the Wiser Hub will fix that and then I'll schedule two hours of downtime for the boiler 1 hour overnight and 1 hour in the daytime I appreciate that the above sounds a bit mental for a WC system but I'm not always at home to see and hear it ramp up but as the Boiler App provides me the total number of hours run and the number of boiler starts I've been noting down the readings every day at the same time so I can see when it's either cycling more than normal or cycle length is shorter than normal

The issue there is the dumb controls are all @EinTopaz requires for the way he uses the heating system

I think I've said this before - be careful if you end up with a DT greater than 20 Deg at the boiler most modern condensing boilers really don't like this much and will do all sorts of things to try and protect themselves. If you are getting a wide DT with a slower pump speed then you could probably lower the flow temp to tighten the DT (at the expense of slightly cooler rads but I wouldn't think the difference in rad temp between 60 and say 55 would be detectable by touch)

I wouldn't expect range rating it down to impact the overshoot unless it was RR down to less than the circuit can accept in which case the temp wouldn't over shoot for a long time - equally the house would be also slower to warm up. Plus your "85%" might be fine for now but when it's -2 outside and you want to throw a bit of heat at the house it could potentially result in a lot slower warm up. IMO the only time you can be justified in RR a boiler is where the boiler capacity is massively in excess of the house heat loss and even then with a scheduled heating (or as and when you think it needs it in your case) you are going to need plenty in reserve to bring the house up to target temp so probably not much point RR'ing the boiler

The other interesting thing is the DT at the boiler On initial start it doesn't apply full power to hit target temp because the DT would be greater than 20 Once the DT is at 20 Deg it applies full power Once the DT starts shrinking it modulates down (it's not doing that by knowing the return temp it doing it based on the flow temp rising above target and then it modulates down At the end of the day you are intermittently heating - your circuit temp at the start is less than 15 Deg C (now the rads will normally be at the same temp as the room when the system has been off for a while so clearly your tolerance for cooler temps is greater than mine or rather Mrs Alien) I do wonder if you would be better of heating low and slow rather than blasts of heat, cool down, blast of heat etc If your flow temp was say 45 deg C and initial circuit temp was 15 the boiler wouldn't have to throttle back and wait for a DT of 20 before hitting the circuit with full power. The return temp would rise and the boiler would modulate down sooner and probably much more........ However with a flow temp of 45 you'd need to have rads that were big enough to emit the heat the rooms needed.

I would think it's managing the modulation based on flow temp target Anyway kWh usage below for the for the two sessions 100% being the first one shows the boiler is really chucking everything it can at the circuit 49% being the second one shows it's modulation percentage is not far out

Similar boiler on third heat exchanger

Not answering for @John Carroll but I'd do readings from start up Logic is I'd want to establish that what the boiler is stating it's modulation state actually was. My 16kW Viessmann modulates from 100% to 10.8% - 100% is 19kW 10.8% is 4.2 kW the % values between the two aren't very linear or put another way if 10.8% is 4.2 kW 100% should be 38 kW

Another thought Read the gas meter at the start and then say every 20 mins noting the modulation claimed Post the readings lets see what it's really consuming

That does appear to be rather odd behaviour How big is the circuit volume?

Then you probably want to give the boiler the ability to run at whatever kW it can or potentially your warm up time will be extended. We used to run a similar process with the old boiler - Summer to Autumn transition - boost for a couple of hours when you feel the house needs it. Moving thro to fixed scheduled heating in the winter months increasing the scheduling period to ensure the house was at target temp when we got in from work Mrs Alien is a stupidly light sleeper and mornings were an issue because if I set the schedule earlier in the morning it woke her so we had to compromise on heating early in the mornings. Then back to boosting whenever required for the spring transition But I found it very unsatisfactory, temps swings, rapid cool down because you aren't putting any warmth into the fabric of the building (so it can't give it back to slow down the temp drop) Needed to heat rooms to a much higher temp to feel the warmth. Moving to weather compensated flow temps enabled me to run lower target room temps - with a little bit of set back on the boiler overnight - house is just so much more comfortable all the time and the additional gas usage compared to scheduled heating isn't worth worrying about (for us it works out to £60 extra a year)

Well despite having a number of hedgehogs thro the garden during the evenings we've only had one take up residence the other one is being ignored. I'll leave it where it is over winter and then maybe relocate it next year as it's probably the location that doesn't suit (no kerb appeal probably)

Saturdays usage in graphical form But you can extract it in 30 min slots in excel format - once you have that you can use HDD data to get a very good picture of your heat loss if heating 24/7 - on a schedule it's not going to be as accurate but it'll give you a good guide PS the peak at 06:00 to 06:30 was my water heating slot

I wouldn’t range rate it at all if heating to a schedule to start with but I’d assess the warm up time and consider range rating only if house heat up was very fast - even then I’d probably not bother with scheduled heating and that’s coming from someone who has range rated boilers in the past but only when they’ve been grossly oversized maybe monitor your gas usage over the winter period and look at it again with a bit of data from octopus (where you can get a massive amount of half hourly data)

Yeah just making a cheaper product range with less functionality with a 24kW condensing fas boiler with a 10kW min that hit the circuit with 65% of max on every restart I had to utilise the anticycle table to manage the boiler fires to a sensible number of cycles per hour - it had a 39 deg min flow temp but it was hopeless trying to run that low 45 deg was just about possible in shoulder seasons but once in winter proper it was 50 or above which meant it short cycled a fair bit

It took me a long time to get my head round the Vaillant/Glow Worm table for anti cycling It's heavily linked to the flow temps used - basically at higher temps you really don't get much anti cycle time at all regardless of what you set the parameter to.

Depends if you are heating to a schedule or 24/7 If heating to a schedule - you really want the boiler to throw whatever kW is needed to bring the house up to temp and you might want the pump to be managed by the boiler. If heating 24/7 - you are just asking the boiler to replace the heat lost (per hour) - in this case range rating (with a margin to allow for extreme temps) and pump speed could be completely different settings wise.

OK seen that now Someone as clever as @John Carroll would probably be able to tell how much kW is being thrown at the circuit based on the flow temp, return temp and flow rate - probably

What's the return temp?

The boiler will be looking at the flow temp and putting in the kW required to keep a steady temp - if it modulated down any more than it is the flow temp would drop Drop the target temp and you'll see it reduce the modulation and then increase it again to maintain the target flow temp. Once the warmer water from the rads start coming back to the boiler - the energy required to maintain the target temp is reduced so at that point it will modulate down further. Till the boiler gets to the point where the temp rises above the target temp and at that point when on min modulation the boiler will allow a certain number of degrees above flow temp before shutting down and waiting for the circuit temp to fall

Next question is how did a HEX get blocked in a relatively new system install? What is the source of the blockage? My concern would be it blocking up again if it is found to be the issue

Exactly my starting point is pretty low already - my flow temps are only good when I'm heating 24/7 - I can get away with a very small set back but the house does need a little solar gain to recover I think it might heat for longer if the boiler responded correctly to being range rated but as it seems to hate being range rated I'm not going to try any more to work with a higher DT at the boiler. House is a comfortable temp all the time so it works as it is System Noise since I fitted the pressure independant TRV bodies is super quiet Boiler doesn't seem to be unhappy with a higher flow rate and a 6 deg DT

Just did some quick an dirty calculations on burn time v HDD ranges At HDD between 0 and 4.9 Boiler runs for 19% of the time so 11 mins in every hour (Sample 10 Days) (in reality it runs for 20 mins in two hours) Between 5 and 9.9 Boiler runs for 35% of the time so 21 mins in every hour (Sample 24 Days) Between 10 and 14.9 Boiler runs for 56% of the time so 33 mins in every hour (Sample 14 Days) Between 15 to 20 Boiler runs for 69% of the time so 40 mins in every hour (Sample 2 Days)