marshian

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