marshian

Just to echo @JohnMo's comments on towel rails as heat emitters when running on low flow temps (Sub 35 Deg C) they really don't cope very well - the design of most towel rails allows short circuit at low flow temps so even if the heat requirements (in a well built house) are really low they almost have same flow temp as return and the heat doesn't rise up the rails it would in a higher flow temp situation. I moved my bathroom towel rails to a downstairs toilet and a utility room and replaced with both with vertical rads (same size but much larger surface area) and fitted with diverters to ensure the flow was spread around the whole rad - heat loss in both bathrooms at -2.5 Deg OAT is ~200 W and at that temp 35 Deg is my target flow temp and the bathrooms comfortably maintain 21 Deg C At T50 the current rads are rated at 900 W at T15 they are 220 W

Excellent progress - I was wondering when the next update would be 😉

I'd be very worried about the floor if that's chipboard flooring - soaks up water very well and once it dries out has the strength of a soggy wheatabix or digestive biscuit!!!! I'd be considering claiming on house insurance and getting it done properly

Nothing is a permanent solution mainly using the opportunity to see if the behaviour can be ironed out Since 01/01/2026 so 62 Days it's done it's ramp up thing 250 times so as an average 4 times a day Quite tempted to pull the spare MBU from it's storage and see if I can extract the code - I'm 100% sure it's firmware driven

It's definitely something like that - only issue is the boiler doesn't have a return temp it does all the management on the flow temp (and possibly the flue temp) Upward temp changes are also a factor - especially when I'm trying to get extended run times. I was toying with getting a clever mate to make me an interface which blunts the changes (basically reads the outside temp sensor but only sends a change in temp to the boiler once an hour)

This was my curve above 10 deg this is my curve Room temp target 13 between 0 and 10 room temp target 17 below Zero room temp target 20 it’s basically as a result of flattening the heat curve to a very small slope and then because the room temp offset changes the curve just using that manually to compensate for the outside temp

Yeah 100% this is something I see and most people wouldn't notice it It's more common between 4 and 8 deg C - after 10 deg it doesn't really happen It hasn't done it for a couple of days since I've changed my strategy for heating and my current WC curves are to to be frank bloody weird......... I'll post them up later but in summary I now have 3 WC curves, one for below zero, one for zero to 10 deg and one for 10 degs and above and I swap between the curves with the target room temp

Well Viessmann technical have washed their hands of the boilers behaviour - their conclusion is that it is normal behaviour for a heat only boiler running weather compensation I'd done a few videos showing the boiler behaviour and shared them with the technical team hoping that this would help to point me in the right direction if it was a set up issue Seeing as they are adamant it's not a boiler issue as such I'll share one here Basically attached a remote microphone to the boiler because the phone itself can't pick up the sound change when it ramps up or down and then filmed the Vicare app on another phone which shows flow temp and modulation level so it's as dull as a dull thing from a content perspective The commentary to go with it is in the description but I'll put it below as well 9.7 Deg Outside Air Temp - Target Flow temp ~25 Deg C Timelines (so you can skip the boring bits) 00:00:20 Boiler Starts (Initial Purge and Burn followed by ramp down) 00:02:12 Boiler at "Minimum modulation" 00:02:47 Running thro the settings (Weather Comp Curve Slope and Level) 00:03:22 thro to 00:15:35 Boiler stable running at min (flow temp slowly rising from initial 27.7 Deg C to 29.2 Deg C) 00:15:37 Boiler modulation increases driving flow temp higher faster 00:17:43 Boiler modulation decreases and then rises again 00:20:18 Boiler modulates back to minimum - flow temps drop to 30.5 Deg C 00:21:45 Boiler shuts down (due to flow temp exceeding target plus 5) 00:21:16 Running thro the settings (Weather Comp Curve Slope and Level)

In an attempt to understand my errant boiler behaviour I recently tried to heat a tank of HW with a 16kW boiler when range rated to 4 kWh - it's only a 115 Litre tank to say progress was glacial was an understatement - a bigger tank would definitely be little and often

I compare it to bashing your own head repeatedly into a wall It's nice when you stop.............

@saveasteading @Nickfromwales@SimonD Alternatively go to your profile Manage followed content Find the "Unfollow" this thread and update preferences

Ahh I wouldn't mind betting we are of a similar era - Good old Fergal I was gonna say @-rick- bravo for persistence but possible you on a hiding to nothing - good luck

Our Meaco when on full Laundry mode is 700 watts but it's very effective and wouldn't be without it

Christ this is hard work - my BH user id is Marshian - You know like from another planet - oh maybe the planet Mars - my better half - Mrs "Alien" (You know like from another planet) I know it's not spelt like that!!!!

I'm just saying start low (ish) and work your way up if the house remains cold - I have this irrational fear that you will start high, pronounce the house too hot, can't sleep and turn it off again People tolerances are different - I'm "hot" above 19 - Mrs Alien - different kettle of fish less than 21 is freezing!!!! Well we can start there - what size and type are the rads and what sizes are the rooms - we have enough knowledge on here to start piecing it all together and come up with a reasonable punt I have a gas boiler and I'm running it like an ASHP - CH 24/7 low flow temps (between 25 and 35 Deg C based on weather comp) - when doing HW it raises the flow temp to heat the tank. I could replace it with a 5kW HP tomorrow and know it would work perfectly - this was the point of my rad upgrades and insulation improvements - get HP ready without leaping into it and then finding all my calcs were wrong and I've got a problem.