marshian

In the interest of discussion I'm going to disagree UK has always lagged behind other countries - The mandating of condensing boilers was done without also mandating how to ensure they condense for all of their operating time - for many replacements they were left on virtually the same settings as the previous non condensing boilers - huge opportunity missed IMO Had I been informed that lowering flow temps would have gained me 7 % efficiency gain the rad changes I have made in the last 3 years would have been done 13 years ago As a result we also missed on getting houses ready for ASHP with lower flow temps which is why you state that ASHP with 55 - 60 deg flow temps and a cop of 3.5 to 4.0 would result in far more conversions but those flow temps and COP is not possible with the current ASHP hardware. I upgraded all my T11 rads to T22 of the same overall dimensions - in terms of output at same temp that's 1.4 times bigger (@T50) - you don't even notice they are bigger - That enabled me to go from a ~60 deg flow to a ~30 deg flow - I am on 22mm circuit with 15mm from circuit to rad but even microbore would would flow enough l/min to ensure the rads were warm enough to heat the house Total spend on rad upgrades was far less than the cost of a boiler change On this point I agree but I don't trust the government to run a bath let alone set a framework for reducing the use of FF

In my case it was 13 years but same reason - didn’t want it to be a distress purchase - knew what I wanted and how I wanted it set up and saw no point waiting any longer

still less than 6 cycles an hour if it’s 8 min burn 3 min coast any boiler is going to cycle more when house is up to temp as it’s only going to need to replace heat lost - good tine to do a few meter reads to give you a goid idea of your heat loss at whateve OAT it is now

If I am right about the kitchen then whichever rad is warmest the lockshield on that rad needs to be wide open - balance the circuit on the lockshield on the other rad. You will still get a drop in temps across each rad but there will always be one rad that has the higher temps If I'm wrong and it is plumbed in normally - ie two pipe than a bunch of your other rads will go cold quickly and your return temp at the boiler will go up

No the opposite - the more open you have a lockshield the more flow it allows - therefore the more likely the return flow temp is higher - the rad may emit more heat but it's only because the meant water temp has increased. It doesn't sound like you need more heat and your boiler doesn't need a higher return temp.

OK a constant flow temp at least means you can see differences in the flow and returns Good You don't want TRV's influencing the flows Ahhh - IMO Not the best time to balance - I know you have all the TRV's open but the rads will have already started to have hotter returns due to warmer room not sucking the heat out of the rads so your delta will be smaller You really want to do it 30 mins after a cold start - enough time to get flows thro all the rads but not enough time that the rooms are warm and are already not pulling the heat from the rads due to a smaller differential between room temp and mean rad temp Good you don't want the TRV's to start messing with the flows With "single panel single convector" T11 rads sized for an 80 deg flow temp it might be conventional wisdom but we really shouldn't be running condensing boilers like that.............. At 55 flow temps best I could get on T11 Rads was 7 to 8 deg On T22 Rads (Double panel double convector) was 12 to 14 Boiler flow temp 55 Boiler Return temp 39 (so overall delta across the boiler was 16 deg) And to do that I had to really slow the flow thro the rads to a point where I needed flow thro the ABV as soon as TRV's started intervening System was much happier with a bit more flow thro the rads lower differences between flow and return on each rad but no ABV until circuit got down to less than 5 rads and very similar delta at the boiler It was at this point I realised trying to achieve conventional wisdom on rad deltas was bloody stupid.....

A thought................ How old is the house - has it been knocked about or extended? I just wonder if part of the circuit has been piped up single pipe configuration (AKA the old way where the rads are daisy chained return from one rad going to flow of another and so on) Nah it couldn't be that surely Then again I look back at some of the temp logging and Kitchen 1 and Kitchen 2 and think ooh the return from 1 rad is the flow temp for the other................ Originally one rad and then another one added without taking the feed from flow and piping up a separate return

Fully open is fine unless the rooms are at 30 deg C they shouldn't intervene Removed just makes 100% sure they don't interfere

The boiler is set up to run on WC for CH with DHWP Only parameters that I have found and adjusted to suit the house and optimise the boiler are only applicable to CH (DHWP are max output (19kWh) and max flow temp (82 Deg C). Max Water Temp Limit 70 Deg C Max Output 40% (so 8 kWh because anything more is not needed - I may drop this further to around 6 kWh) No Anti-cycle parameters that I have found Pump Over run is non adjustable (set to a 3min max from factory) I'd attach the Installation and operation manual but it's too large but a google for Viessmann 100-W B1GA should get you to a copy The Valliant (Glow worm) Anti-cycle parameters took me for ever to get my head around but once I did it was very useful and getting a 24 kWh boiler with a 10 kWh min to work much better with less cycling! (mainly because I was also using pump overrun to manage the time between burns as well)

My flow temp last night at 6 deg C was 30 deg C The boiler over the course of 15 mins gradually went over target temp at min modulation 10.6% (3.2 kWh) by 4 deg in order to extend the run time so finally shut down at 34 Deg C I wasn't busy so watched my temp sensors for the 20 mins it coasted (pump running boiler not firing) and it re-fired shortly after this picture was taken. Left side display is flow temp Right hand side is return temp I'm pretty sure my boiler doesn't follow the flow temp - 5 deg rule My previous glow worm boiler didn't either

Yeah it may well be but the boiler is reacting to the temperature it gets from the internal sensor.........

Hmm OK I'll defer to your knowledge but I think 5 deg delta from flow temp is really bloody narrow at 60 deg flow temp - especially as on that flow setting the boiler is getting no benefit from the condensing process with a return of 55 The glow worm I had would only re-fire when return temp = flow temp (typically with a 50 deg flow temp return needed to get down to 31 (ish) before the boiler fired Same with the Viessmann I have now (trouble is I'm running much lower flow temps but a 30 deg C flow temp it re-fires when it sees no difference between flow and return temps which is around 24 deg C (I thought this was because most of the heat in the circuit had been extracted)

But you said you set it to 60 flow and at 56 return it fired up? I realise that 60 = 65 when boiler coasts but I would expect a 60 deg set point to relight at 50 deg not 56

That's not a lot of difference between flow and return for the boiler to re-fire??

Same here all the windows and doors replaced with PVC double glazed back in 1994 still got them 30 years later - glazed units might not be up to current regs but they all still seal perfectly no leaks or drafts - never had a single glazed unit fail and they haven't gone yellow either but they were the best quality units we could find. Neighbour is on his 3rd set of windows and doors and he's only been in that house 20 years - first set to replace aluminium framed originals, they went yellow in a few years and then one by one the glazing started failing - most recent set has already had glazing units replaced Buy cheap rubbish you need to buy it more often

But it’s not being used as a buffer - it’s being used as a volumiser - useful link tho will read it properly later I considered fitting a volumiser with my old boiler to aleviate some of the short cycling issues I had (resolved instead by replacing the boiler with one that had a far better turndown/modulation) My intention was to fit it to the hot side so after the boiler hit the overheat limit the volume of water that needed to pass thro the rads before the restart temp was reached would be higher than the circuit without a volumiser but I had a flow rate of 10 lpm so With a few rads in circuit and the volumiser the total volume before the return temp dropped down to the flow temp (aka boiler restart time) I would have had maybe 6 or 7 mins of coast rather than 3 mins. However once I worked out the valliant/glow worm anticycle settings I could force the boiler to wait so no more need of a volumiser

Oh that's odd - I would have expected the volumiser to be on the hot side of the boiler not the cold side but I guess it doesn't matter

Thinking about it that's a heck of a circuit temp drop in 3 mins 65 deg down to 50 (ish) Have you got an ABV in the circuit?

My Heat only 16 kW 100-W Viessmann (so 3.2 kWh min output) when OAT drops to 0 deg C will happily run for 100 mins each burn at a flow temp of between 30 to 32 deg C Return temp is 24 to 26 Deg C

@JohnMo has an ATAG from memory

If in 60 mins you have 30 mins of burn, 3 mins of flame out and then another 27 mins of burn (in the hour) I would not call that short cycling - but that's just me............ If you had 3mins of burn and 3 mins of flame out and that process is repeated throughout 60 mins so that it's 10 burns in that time I would call that short cycling and badly short cycling at that. Ahhh explains it My question is if the rads are rarely used why are you using an elevated flow temp much higher than the floor needs and mixing it down - why not set the flow temp much lower (or as low as you can get it - like 45) it makes no sense to me to heat the circuit to a higher temp than the circuit is set too If the rads are required due to OAT being low then just increase the flow temp when the rads are required I'm not sure you need to do that based on my comments above Incidentally I'm all rads no underfloor and my boiler is currently at a flow temp set point of 29.4 deg C, since midnight last night (or this morning depending on your viewpoint) with the heating demand being 24/7 with no setbacks the boiler has been on for 780 mins - it's fired 21 times today with an avg burn time 37 mins. I have no volumiser or buffer as the circuit size is 130 Litres with 100 Litres being the volume in the rads and the boiler will modulate down to 3.2 kWh

Only if you want too - but towel rails are normally bypass rads because towels take longer to dry and bathrooms with towels over the rads take longer to heat. If you do fit them with TRV's you'll need to make your ABV less restrictive If you are happy the valve isn't allowing flow thro it due to an aging spring and the temps are very different either side then - my ABV has a scale with a number of points on it from 0.05 bar to 0.5 bar and it takes about thirty turns to go from 0.05 to 0.5 bar so I'm not sure how one with 0-5 numbers each 60 deg apart would work - I've tried google image search but not found anything similar Not sure why the focus on 12 Deg but I've said that before OK get a plumber to look at it It should only be a similar temperature to the water circulating thro it Seen them and responded

Quick fire questions Boiler flow temp still 60? All TRV's (where fitted are wide open) for a decent period of time say 30 mins after heating first came on before you took the readings? Because I'm now checking everything - You took the readings in the warm up phase - ie not when the rooms were up to temp and every room was cosy? Still don't know why you are trying to target 12 Deg delta on all the rads? Also don't know why you can't understand a really simple point The "hot" end of a rad is the "flow" and the "cooler" end is the "return" It doesn't matter if the hot end has a TRV or a lockshield at that end it's still the hot end therefore the flow - when you insist on putting the higher temp reading as the return value and the lower temp reading as the flow it makes no sense whatsoever. In the case of K1, Loo, Hall and Bed 4 you are declaring that the water in the radiators are being warmed up by the temp in the room because the return is higher than the flow - if that is the case then I think your room temps are too high

I might not be following but you've only got the volumiser (Buffer) in the underfloor circuit and one rad - not the rest of the rads?? I had huge issues with my glow worm boiler cycling (24kW - min output 10kW * see note) house heat loss after improvements 4.2 kW at -2.4 Deg C any warmer than that and it was going to cycle - shoulder season it was 3 mins on 3 mins off What I found helped was the anti cycle setting (on glow worm it was also related to flow temp) - does your boiler have that parameter - because if it does you can basically force the boiler to wait longer between burns so the circuit cools more. Obviously if the house isn't getting warm because of the anti cycle parameter then you need to reduce it but I found it very useful in managing the cycling issue Note * on initial fire it was throwing 85% of the max at the circuit so if the circuit was small it was overshooting and shutting down

I do it all the time when decorating no leaks or issues - obviously only works with conventional rads (fed bottom in bottom out) and not towel rails or vertical rads but that's life Only one rad in the house has no pull up clearance so I can't on that one but all the rest have a good 5 - 10 mm of "pullupability"