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Pm him I am sure he will have a explanation
You will get particles that will build up in the burner chamber that won’t get flushed through with the condense and will build up to a point where it just blocks the hex and could cause it to split
Like this
 

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That does make sense, but wonder how many condensing boilers are actually running in condensing mode ? Maybe apart from new installs 🤔 mine not been condensing since new in 2009, only since January 2021 have I been trying, but still not a great success, minimum return temperature 53-55oC, only thing I can do is replace two lounge radiators with double fin, each would then give approx 30% extra heat output ( 100cm x 50 cm )
 
I am sure it will be condensing at certain times of the day, I by no means have John G' s grasp of the figures but I have 80 + boilers on my books which I service and maintain, and where possible I advise my customers to keep the flow temperature setting at 65° c by keeping the heat exchanger clean serviced correctly and that means a full strip and clean every year flushed though electrodes cleaned condense trap removed and fully cleaned or replaced any small leaks addressed gas valve adjusted , every 5 years the system drained flushed and a good quality inhibitor added I rarely get a breakdown from doing a flue gas analysis which we do on each service you can determine efficiency at different stages of firing , modulation, and flue gas temperature I personally think you have probably got your system running the best you can without changing things replace radiators for larger ones by all means this allows you to run the system at a lower temperature and still be comfortable in your living space. Regards kop
 
The boiler will certainly condense very heavily on start up in the morning where it might take a 18kw boiler ~ 10 minutes to heat say 75 litres of water from 20c to 50C, also if the house/room temp is very cold then a certain amount of condensing will also take place.

Its interesting though that if you have a fixed flow temp of 65C and a flow of 0.75m3/hr (fairly normal for a 18/20 boiler) then no matter how oversized the rads are that the return temp cannot be lower than ~ 51C once the rooms are up to temperature (I use 23C) the room temp and the return temp will then start rising.
I spoke to a (long retired) acquaintance of mine earlier on and he said he never remembers measuring a gas fired boiler flue gas temp below 55C, what kind of flue gas temps are you seeing KOP?.
 
I am working on one now as we speak
 

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Boiler NO 81? should now be be running at 65C/0.39M3/hr (flow) and rad(s) output of 59% OR
55C/0.77M3/hr (flow) and rad(s) output of 48%.
and Shaun's condensate flow at roughly 0.7 lit/hr @ 20 kw boiler output or pro rata.
 
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I thought the same thing as John mentioned, when the boiler first fires up in the morning, return temperature is typically 20-25oC & after it cuts out on the room stat, may not restart for 1-2 hours, then again very low return temperature for some time ( will try and monitor return temperature next time it restarts, be interesting to see the climb rate and how long it ‘ should be’ condensing for. So going back to deposits on the heat exchanger wouldn't these periods of heavy condensing keep the exchanger clean ? I am running my boiler outlet at 64oC, i tried 62oC, but even 2oC seemed to make noticeable difference to radiator heat output. The return temperature when steady and modulating is 53-56oC. As I said previously I was considering replacing 2 lounge radiators with double fin, but looks like the best I might get is a 45oC return temperature.....only an educated guess.....which would give a 3% saving, would take around 20-25 years to pay back the cost..so very likely going to abandon that idea.

I know I may get shouted at, but I dont suppose I could clean the heat exchanger myself, I think it will need a Gas Safe person most likely.......

there is a move to make manufacturers add an efficiency display to their boilers and show when it’s in condensing mode, I think they will fight hard against this, as people will soon realise they are not getting the 97% efficiency that they expect..

take care all & keep safe 😎
 
I maybe thinking wrong but how can 2dc make a room feel colder when it’s well above the room temperature

I could understand if the flow temp was 40 but not 60dc you sure you have a flow temp at 62dc at all your trvs ?
 
I maybe thinking wrong but how can 2dc make a room feel colder when it’s well above the room temperature

I could understand if the flow temp was 40 but not 60dc you sure you have a flow temp at 62dc at all your trvs ?
Hello, there must come a flow temperature that just doesn’t release enough heat to be comfortable, not sure if flow temperature and radiator heat release is linear. Just seeemed to make a difference when I lowered it to 62oC.....no idea if its the same temperature at the TRVs all rads do get hot, so assume that must be the case.....

also at 62oC the boiler often cuts out at 65oC as it can’t reduce below 5KW......

very happy with how it’s running now, have had some excellent advice and learnt lots in the process.....

thanks
 
This thread has thrown up some extraordinary "facts" re flowtemps/flowrates and their effect on return temps etc.

Any temperature change in either flow or room temp will have a effect on rad output but its not linear, it works with a exponent of 1.3 where the rad output is based on the ((meanradtemp)-requiredroomtemp))^1.3.

Using your observations above, initially I calculated that the 4/5 rads that you have running at a fixed flow of 0.76M3/hr......
flow/return/rad output 65C/59C/5.21kw. Now reduce the flowtemp to 63C results in........
63C/57.4C/4.9kw (which is why your boiler is cycling), you are running right at the switch point because you require the rads to run at ~ 68% of their rated output so running very close to the minimum boiler output.
If you require a rad output of 5.21kw with that 63C flowtemp then the flowrate would have to be increased from 0.76M3/hr to 2.24M3/hr, (impossible) and you would achieve 63C/61C/5.21kw.

If you had TRVs on these rads and increased the flowtemp to 75C then they would have throttled in to give 75C/48.8C/5.21kw at a very reduced flowrate of 0.17M3/hr. rad&boiler deltaT of 26.2C, OK if boiler is running but flow too low for the 1 minute fire up requirement of 9.6kw.

The above might look a bit complicated but very easy to calculate in a spreadsheet I made.
 
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Should also add another bit of info.
If your room(s) should suddenly fall to 10C then the flow/return/output will be
65C/56.6C/7.35kw. 5C roomtemp = 65C/55.6C/8.21kw & 0C = 65C/54.4C/10.6kw.
The most interesting part of all this is that the return temp doesn't change much in any of the above so it looks like any system with fixed flow temp and fixed flowrate will never condense under any conditions except at start up
 
Very interesting John, would love to see the spreadsheet, always making these for all sorts of things......thanks
Should also add another bit of info.
If your room(s) should suddenly fall to 10C then the flow/return/output will be
65C/56.6C/7.35kw. 5C roomtemp = 65C/55.6C/8.21kw & 0C = 65C/54.4C/10.6kw.
The most interesting part of all this is that the return temp doesn't change much in any of the above so it looks like any system with fixed flow temp and fixed flowrate will never condense under any conditions except at start up
interesting stuff 👍 would love to se your spreadsheet, can you attach ?
 
I will try once again but for the past few months havn't been able to attach any, they used to attach no problem previously in zipped form.
 
King of pipes talks about a service which includes cleaning out the heat exchange, plus effi checks etc etc, is this common for all boiler services ? I have heard some services only cover the very basics. ‘hands in air’ have not had a service since 2010 ( 1st service) think maybe a good idea to get a good service me for piece of mind and to see how the heat exchanger is doing, but finding a good one isn’t easy, unless i use trust a trader maybe....the link on this forum says none found for my postcode.
 
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I definitely think you need a full strip down a good service an a gas safety check your boiler should look like this when stripped , the heat exchanger had to come out on this one to repair a leak behind it . Kop
 

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I normally charge 150-200 depending on parts required

every 5 years Maximum between normally do them every 4 years
 
£ 150 + parts this should be done every year a G10 burner seal kit is a must, get a flue gas analysis done before then after your service it will be interesting to see the figures plenty of engineers still working look on the gas safe website for ones in your area . 😉 Kop
 
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Very interesting John, would love to see the spreadsheet, always making these for all sorts of things.***..thanks

interesting stuff 👍 would love to se your spreadsheet, can you attach ?
Couldn't attach spreadsheet (or any file for that matter) but here is how I did it in one simple line.

1615145367157.png
 
Will look for a Gas Safe engineer, but £150 seems so expensive. Guess it’s the cost of maintaining the Gas Safe certification. I know it sounds bad, but having not had a service for 11 years, I have saved £1200- £1600, enough to now have a new boiler installed. I absolutely know you will disagre, but I have a CO detector fitted next to the boiler, so hopefully that will warn me if the worst happens, but obviously don’t know if it’s efficiency is being maintained. Although gas use is fairly constant over the years.
 
Will look for a Registered Gas Engineer, but £150 seems so expensive. Guess it’s the cost of maintaining the Gas Safe certification. I know it sounds bad, but having not had a service for 11 years, I have saved £1200- £1600, enough to now have a new boiler installed. I absolutely know you will disagre, but I have a CO detector fitted next to the boiler, so hopefully that will warn me if the worst happens, but obviously don’t know if it’s efficiency is being maintained. Although gas use is fairly constant over the years.
Yes I am afraid i do disagree I suggest you log onto the gas safe website there is so much information available, help and advice the costs involved will vary widely across the country but don't forget the cost of the work is not all going to the engineer it costs us a fortune to get registered to be able do even do our job, then there's testing equipment tool costs, public liability insurance, calibration costs of the equipment, 20% to 40% goes in tax, vehicle costs , tax, insurance, mot, maintenance , internet cost , mobile phone cost, theres a awful lot to be paid out of that £150 .
If you are a carer for your wife and receive some sort of benefit you may qualify for a free gas safety check contact your energy supplier for details.
Your boiler will not operate safely or efficiently unless it is serviced and maintained correctly, all you are trying to achieve is not going to happen and all the adjustments are a waste of time in my opinion, Get a full service and gas safety check asap, keep yourself and your family safe . Regards Kop
 
Yes I am afraid i do disagree I suggest you log onto the gas safe website there is so much information available, help and advice the costs involved will vary widely across the country but don't forget the cost of the work is not all going to the engineer it costs us a fortune to get registered to be able do even do our job, then there's testing equipment tool costs, public liability insurance, calibration costs of the equipment, 20% to 40% goes in tax, vehicle costs , tax, insurance, mot, maintenance , internet cost , mobile phone cost, theres a awful lot to be paid out of that £150 .
If you are a carer for your wife and receive some sort of benefit you may qualify for a free gas safety check contact your energy supplier for details.
Your boiler will not operate safely or efficiently unless it is serviced and maintained correctly, all you are trying to achieve is not going to happen and all the adjustments are a waste of time in my opinion, Get a full service and gas safety check asap, keep yourself and your family safe . Regards Kop
I would love to be able to afford £150 a year to get the boiler serviced, but it’s a balancing act when relying only on a basic pension. There’s always some thing that needs money thrown at it. Also my health isn’t what it used to be and have to pay tradesmen to do jobs I would have done so easily just a few years ago, getting old is really no fun at all 🤯
Yes I am a full time carer for my Wife, so maybe I do qualify for the Gas safety check, what exactly does that involve ? I assume it’s simply a CO reading around the boiler, or is it more ? It’s a pity Gas Safe registration is so expensive, as you say there are so many other expenses. my local plumber has given up being Gas Safe, purely from the costs involved.
good luck and keep safe
 
Its all on the gas safe website my friend and I know it's no fun getting old if you were local to me I would do it for free and I often do when situations like yours come along , there may well be help out there you just need to ask don't be to proud we a need a little help now and again 😉
Kind regards kop
 
Couldn't attach spreadsheet (or any file for that matter) but here is how I did it in one simple line.

View attachment 48157
I know condensing isn't top of your list at the moment but thought I'd post the following.

I first of all carried out a quick test on own 20kw oil fired system, I set the boiler to give a average flow temp of 65C. I then opened all the TRVs fully and rather than spending hours trying to get a deltaT of 20C across every rad I simply throttled in a (one) valve on the main return before the pump and fairly quickly got 20C deltaT, (65C/45C), I then reopened the valve fully again once I was happy that I could achieve this without any problem.
With this in mind, I then did a few calculations based on a total rad output of 20kw with two zones (not HW) opened and with one zone only with a output of 10kw.
20kw rated output gives a actual output of 12.6kw with flow/return of 65/45C and a flow of 0.54m3/hr.
10kw rated output (one zone) gives a actual output of 7.3kw with flow/return of 65/53.5C at the same flowrate.
This is the basic problem with the above fixed parameters, once you switch down to one zone then no more condensing, like in your case.
The choices then are, 1, live with it. 2. use TRVs which will give condensing most/all of the time. 3. reduce the flow temp when on one zone (or both).
For example, with two zones if you reduced the flow temp to 55C with both zones (but original flow of 0.54m3/hr) output 9.3kw, flow/return of 55/40C, reduce further to 45C, output 6.1kw, flow/return of 45/35.3C.
One (10kw) zone, reduce flow temp to 60C, output 6.3kw, flow/return 60/50C (just condensing)
reduce flow temp to 55C, output 5.3kw, flow/return 55/46.5C.
reduce flow temp to 45C, output 3.5kw, flow/return 45/39.5C.
All calcs carried out with room temp of 20C.
 
I asked a poster on another thread to monitor the boiler stat hysteresis on his 11 year old Vaillant Ecotech 37kw system boiler,

"The flame is on and the boiler temperature rises until it is about 4 or 5 degrees higher than the set point and then goes into pump overrun. The flame goes off and the system cools to around 8 or 9 degrees below the set point, pump overrun goes off and then flame on to start heating again."
 

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