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Misterdog

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Rorschach

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You have no option, condensing mode is dependant on the system.
Something to do with the temperature differential on the flow and return pipes.
Just looked. my boiler has been on for 6045 hours of which only 57% was in condensing mode.


Strangely when selling you a new boiler they only focus on the 90% +
figure.
Sorry I thought you meant not have in on the condensing setting. Yes of course the boiler may not always work at full efficiency, but it's still going to way exceed a 60yr old boiler.
 

Misterdog

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Indeed. There is no 'condensing setting' the boiler can only condense when certain conditions allow it to do so.
Though turning up the boiler stat reduces the time in condensing mode
(system dependant). I fitted weather compensation control which alters the stat automatically depending on the outside temperature.
I can tell how cold it is outside as the radiators get hotter.
The boiler has paid for itself in gas savings over 3 years, though I installed most of it myself.
It's an Ideal boiler which is superbly engineered, it has a processor and screen which gives me the information about burner time and efficiency level.
Far better than the Worcester Bosch I had before.
 

Rorschach

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Indeed. There is no 'condensing setting' the boiler can only condense when certain conditions allow it to do so.
Though turning up the boiler stat reduces the time in condensing mode
(system dependant). I fitted weather compensation control which alters the stat automatically depending on the outside temperature.
I can tell how cold it is outside as the radiators get hotter.
The boiler has paid for itself in gas savings over 3 years, though I installed most of it myself.
It's an Ideal boiler which is superbly engineered, it has a processor and screen which gives me the information about burner time and efficiency level.
Far better than the Worcester Bosch I had before.
On our ideal boiler there is a condensing setting for the temperature, it sets the water temp to 65c, the optimum condensing temperature. Of course I accept that this still may not mean it can work to full efficiency all the time.
 

Misterdog

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Basically a boiler stat then, I suspect 65c would not be enough for my 160 year old house, especially as some of the radiators were installed in the 1970's.....
 

NormanB

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Measuring the temperature difference at the feed pipe to the coil and the return from the coil at or towards the end of a cycle will tell you what is going on.

However, from what you have described the primary circuit is fouled and will require flushing, cleaning and inhibiting. This would also be a mandatory requirement prior to fitting a new boiler.

Given the age of the system AND if you live in a hard water area, the hot water side of the coil is likely to be heavily scaled. If that is the case the only practical/cost effective remedy is a new cylinder. So, a double whammy mitigating heat transfer on both sides of the coil.

If you know the history of the system - it is most unlikely the circulating pump is still doing the business - most will have given up the ghost at circa 20 years. Given the state of the primary circuit water adds grist to that mill.

However and all that being said. I have just looked at your photo again and there is no way the hot water cylinder is from the 1960s. I doubt judging by the energy label it is very old at all - when did those ‘labelling standards come in 2000+?

So that must shed some doubt on the age of the boiler I really doubt it’s is from the 60s’ - can you get make and model number serial number and do some googling. Likely to be similar age to cylinder methinks.
 
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Glitch

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Need the return temp at 55c or less to get it condensing. Too high a flow temp can make it less efficient as it returns higher than 55c.
Seems there is an art to tweaking condensing boilers for maximum efficiency. Most installers don't understand it, allegedly.
Also it seems most installers over-spec the power of replacement boilers - apparently that can work affect efficiency too.

My Vaillant boiler was cycling too much when first installed. The replacement (energy efficient) pump wasn't man enough for the job so that got swapped for one with more grunt, plus the temp was reduced to 72c.
I'm reading on t'internet that 60c-65c is better. Going to try 65c and see what happens.
Also found the code (17) to enter installer mode. It gives you loads of additional data including return temp.
 

Misterdog

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The bigger the radiators, or preferably underfloor heating, allow the return pipe temperature to be lower and hence in condensing mode more often.

Flow temperature - house heating 'loss' = return temperature.

It's not as simple as turning the flow temperature/boiler thermostat down.
During really cold weather radiators need to run hotter to maintain a given room temperature.
One of the worst things people do, is turn up the boiler stat, in cold weather, and forget about it.


Max Efficiency
For the condensing boiler to operate at maximum efficiency, the secondary heat exchanger’s surface needs to be equal to or below the dew point temperature of the fuel used. This is the temperature at which water droplets form. For natural gas boilers, the dew point is around 55C. In other words, the water in the return pipe needs to be 55C or lower or your boiler will not operate at maximum efficiency and potentially will not even condense.

Turning down the temperature on your boiler can help increase its efficiency. Most modern boilers will have a mark on the screen that shows you the point at which condensing mode will be turned on. For example, on Ideal Logic+ boilers, there’s an ‘E’ icon on the central heating dial, which is 68C.


There are factors that will affect this. For example, if you have smart heating with individual radiator valves, such as with the Honeywell Evohome, the return temperature can change. For example, if you’re heating the entire house, with all valves open, you’ll get a cooler return. If you’ve only got one radiator valve open, the return will be warmer.

However, the benefit of only heating a single room will mean that your boiler will shut down sooner, so the overall energy savings will be higher. For the best energy savings, a thermostat and boiler that can use OpenTherm will work best, as this lets the thermostat adjust (modulate) the water temperature for the best results.
 

Spectric

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To get a condensing boiler to run in condensing mode the return temperature has to be low, around 55° C and to achieve this you must correctly size the radiators. Also they can be more efficient in newer instalations where full zoning has been applied through design, so all rooms can achieve the required temperature as they each control the boiler via a stat & zone valve. Gone are the days where there was just a stat and often the boiler just cycled.
 

Jos7000

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To get a condensing boiler to run in condensing mode the return temperature has to be low, around 55° C and to achieve this you must correctly size the radiators. Also they can be more efficient in newer instalations where full zoning has been applied through design, so all rooms can achieve the required temperature as they each control the boiler via a stat & zone valve. Gone are the days where there was just a stat and often the boiler just cycled.
Gone for the majority, but not everyone.
My ideal elan, works just fine and I have no intention of scrapping it.
 

Jos7000

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I do indeed, except in the warmer months following a high wind. I only use my boiler for heating, not for hot water.
Standing charges mean I pay the same for a pilot light as I do for zero usage.
 

mikej460

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It does sound as if the system is clogged, which isn't surprising given its age. A word of warning that a professional flush is very expensive (I seem to recall paying £400 in 2006). Given the potential energy cost savings you might want to think hard about a replacement boiler, but investing in a visit and advice from a heating engineer would be wise. Our neighbour started to have problems with their old boiler and the engineer basically condemned it. They had a new energy efficient model fitted together with TRVs and halved their fuel cost in the first winter. They live in a 300 year old cottage.

This article might be helpful
Boiler Grants: Can I Get A Free Boiler? - Which?
 

Sandyn

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If you want to try to hold on to your system, It's easy to flush out a central heating system. It's something you could do yourself. It may not give as good results as a power flush, but it will do enough to get it going again, assuming that is the problem. Will give you time to look at alternatives.
 

croft36

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do you know for sure that it's burning the same amount of gas or oil (whatever it normally would) when it's on? If it's oil, is there a chance that an injector is clogged?
Gas consumption is the same as in 2019 when the boiler was performing as expected.
 

croft36

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Woah your numbers are way off there. A modern condensing boiler can be over 90% efficient, some almost 99%.

An old boiler from the 60's would have been lucky to be 50% efficient when new, dread to think how bad it is now.
My boiler Crane Cavalial
Woah your numbers are way off there. A modern condensing boiler can be over 90% efficient, some almost 99%.

An old boiler from the 60's would have been lucky to be 50% efficient when new, dread to think how bad it is now.
The boiler specification is input 80,000btu/h, output 60,000 btu/h which I took to equate to 75% efficient.
 

Jos7000

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It does sound as if the system is clogged, which isn't surprising given its age. A word of warning that a professional flush is very expensive (I seem to recall paying £400 in 2006). Given the potential energy cost savings you might want to think hard about a replacement boiler, but investing in a visit and advice from a heating engineer would be wise. Our neighbour started to have problems with their old boiler and the engineer basically condemned it. They had a new energy efficient model fitted together with TRVs and halved their fuel cost in the first winter. They live in a 300 year old cottage.

This article might be helpful
Boiler Grants: Can I Get A Free Boiler? - Which?
I'd be interested to know the actual figures in relation to expenditure for modernising, presuming their condemned boiler was very old.
My point being, sometimes the outlay takes decades to recoup in fuel savings. Double glazing isn't always the investment people think and loft insulation can take twenty years if you have to pay for it.
My system is open, modern pressurised systems would most likely require the replacement of the majority if not all of my system. Yes it would be cheaper to run, but at what cost to replace and maintain?! Modern boilers really can't last as long as much older versions and are often much less reliable.
 

Glitch

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My boiler Crane Cavalial

The boiler specification is input 80,000btu/h, output 60,000 btu/h which I took to equate to 75% efficient.
It could now be the oldest working boiler in the U.K. 🤣

 
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