Keeping a boiler in condensing mode

CashStrapped

You would think that, but you are assuming that the boiler is able to condense 100% of the water vapour produced, which I do not think would be likley, so there will always be some extracted via the flue.

That is only a theory based on what I have read.

Now, I would not assume that because you can see steam coming out of the flue that it is being run at it's most efficient. As I said, the fact you can see steam, means a lot of the heat has already been extracted, but the exhaust gas is still warmer than the air outside. The fact that it is mcuh cooler means it turns to steam much quicker.

However I would not just use the flue as a sign of efficiency.

CashStrapped

Double post - ignore

Andy_WSM

CashStrapped wrote: »

However I would not just use the flue as a sign of efficiency.

I'm not claiming my boiler runs as efficiently as possible, but the vapour being visible out of the exhaust is THE ONLY sign I have that it is condensing. That's the point of this thread isn't it? Cardew is asking how we should keep our boilers in condesning mode - and I've posted the only way I know.

As the boiler is in the loft, fiddling with it every time the weather changes or the number of rooms that need heating changes isn't going to happen!

I'm not convinced condesning boilers are any good and my plumber tells me they break a lot quicker than ye olde fashioned boilers due to very complex electronics and the condense being acidic, which rots them from the inside out.

Cardew

lstar337 wrote: »

Now, to try to redeem a little of what I said in that earlier post:On my boiler the 'e' position is over 3/4 of the way around the dial, which to me is 'high' at a glance. (Stupid boy) In reality, it is 'economy mode' which is lower down the scale than the graphic on the boiler suggests. It is the point at which the boiler uses all of its bag of tricks to keep itself in 'condensing mode' (modulating the flame and keeping the outgoing temperature at a level which keeps the return low enough for that 10% efficiency boost) for that 95% of the time.

It is my understanding that modulating the boiler output does not affect the outgoing water temperature. i.e. if you have the water temperature set to, say, 60C, the boiler output modulates to keep it at 60C regardless of the demand(no of radiators) the boiler is supplying.

daveyjp

Cardew wrote: »

It is my understanding that modulating the boiler output does not affect the outgoing water temperature. i.e. if you have the water temperature set to, say, 60C, the boiler output modulates to keep it at 60C regardless of the demand(no of radiators) the boiler is supplying.

Correct, but the previous poster must have an economy setting, labelled 'e'. The boiler will modulate to keep the temperature at whatever the preset 'e' temperature is.

My boiler info suggests fitting a weather compensator as this then sets the central heating circuit temperature to the most efficient level based in the external temperature.

Without one it suggests changing the CH water temp to reflect the outside temperature. It usefully gives no information about the temperature to set CHW on based on external temperatures! I.e extrernal temp 12 degrees, CHW 60 degrees etc.

lstar337

I was looking at the boiler this morning to see what it was doing, and noticed something I had not noticed before. While running the heating I spotted that frequently (but not the whole time) 'High Efficiency' was displayed on the LCD. I assume this is when it is condensing.

If I cranked the temperature down a little I was able to get 'High Efficiency' to stay on the screen the whole time. I will probably leave it like this as it had no noticeable effect on heating the house.

Cardew

Presumably at this time of the year your heating load is not high.


Assuming your High Efficiency display does indicate condensing mode(which seems a reasonable assumption) it would be interesting to get some observations on a very cold winter's night when the heating load is heavy.


As a matter of interest what happens to the display if heating is off completely and hot water is being demanded? It obviously shouldn't be on at all.

lstar337

Cardew wrote: »

Presumably at this time of the year your heating load is not high.

Yeah, it was very low (and off now). I just put it on for 15mins at 6am to take the chill off the bathroom for SWMBO. I believe 3 or 4 other radiators are also active but set at a low level.

Cardew wrote: »

Assuming your High Efficiency display does indicate condensing mode(which seems a reasonable assumption) it would be interesting to get some observations on a very cold winter's night when the heating load is heavy.

Indeed. The manual states that the level above the 'e' on the dial may need to be used during prolonged periods of cold weather. However, our building is A rated so I don't expect the heating demand to ever be that high. I guess a very cold winter will be needed to put that to the test, and I just don't see that happening this year.

Cardew wrote: »

As a matter of interest what happens to the display if heating is off completely and hot water is being demanded? It obviously shouldn't be on at all.

It says 'Hot water' followed by 'Temperature 55c'.

Interestingly the manual says that in DHW mode the display will show 'Hot water' followed by 'Temperature *c' followed by 'High efficiency' (If conditions are suitable). *value set by user.

Which seems to indicate that it can operate in condensing mode for DHW under some circumstances. There is no indication that I can find of what these conditions are. I may keep an eye on the display next time SWMBO is having a shower to see what it does.

Cardew

lstar337 wrote: »

It says 'Hot water' followed by 'Temperature 55c'.

Interestingly the manual says that in DHW mode the display will show 'Hot water' followed by 'Temperature *c' followed by 'High efficiency' (If conditions are suitable). *value set by user.

Which seems to indicate that it can operate in condensing mode for DHW under some circumstances. There is no indication that I can find of what these conditions are. I may keep an eye on the display next time SWMBO is having a shower to see what it does.

To me that would indicate the 'high efficiency' display doesn't indicate condensing mode.


I have been looking at the latest 'Which' review of boilers and even for the best buys combis with the highest CH efficiency, the Hot Water efficiency can be as low as 50% - 60%.


So as stated above if the 'high efficiency' display doesn't indicate condensing mode for Hot Water, I would now surmise that it also doesn't indicate condensing mode for heating???


P.S.
In days of yore you might have been keeping your eye on SWMBO in the shower, rather than the boiler!!

Cardew

Incidentally your combi display is indicating 55C for hot water only? That is sufficient to scald in a shower the maximum recommended is 43C. - I appreciate it can be mixed with cold water.


Also most combis only give figures of flow for heating inlet water in the region of 30C - bearing in mind the inlet water temperature can be below 5C in winter.