E is Low Temperature Mode apparently - where it’ll heat up to around 75 Celsius. Use with caution.

Hmm - that’s not low !!

I think they mean cold weather. :)

This dates from a recommendation before more recent research 

Do you know what the hot water temperatures are at the different settings ?

Your wish, is my command.

Theoretically they’re here .. but the engineer can change these on installation 

Ah. The attachment is for a different model. It’s the temperature of the domestic hot water that I’m interested in. The ‘e’ is only on the ‘tap’ dial so I wondered what temp that was, and where the dial should be set for tap water at 50 deg C.

Without matching the exact model it’s difficult to tell although for hot water, 3 is meant to be 60deg

‘e’ for economy (or efficiency) perhaps?

Condensing boilers are at their most efficent at around 50-55 C water output temperature.
So going to a lower temp can be less efficient, just as going higher can be.

Personally, like many people, I like my hot water (and radiators) to be a bit higher than that at around 60 for the tap and 65 for the radiators

This is a good video about it although it is more about radiators than the tap water (because the radiators are usually on for longer than a tap): https://www.youtube.com/watch?v=T022zY9I__0&ab_channel=TheHeatingHub

Or just try it at the tap and adjust it to what feels OK once the tap has been running for 30 seconds or more. (Careful not to scald yourself, start cooler and work up).

Remember that for a mixer tap or a shower then how cold the cold water is (how cold it is outside the house) will make a difference to the temperature after mixing.

Hello ​@juliamc,

on my greenstar 8000 the eco button refers to hot water preheat. I.e. there is water in the hot water heat exchanger which cools while unused. Non-eco mode fires up the boiler at intervals to keep it warm and reduce the “cold slug” of water when you turn the tap on. Eco mode leaves it go cold. TBH with our long pipe run I don’t see much difference.

Hey ​@juliamc,

Great question and I can see it’s brought out a lot of great support from the community 

Do you want me to convert the thread to a question so we can assign a best answer when we have one? 

Sorry I’m going blind. I couldn’t see the e on the dial.

Likewise - I didn’t notice that ‘e’ on the dial ! This is a friend’s boiler so I don’t know how hot their water is. With our heat pump we have a tank of hot water at 50 deg max, and that’s hot enough for us.

Thats v useful to know the temperature that the condensing happens so I’d say ​@Nukecad ’s answer is best so far ! But I can’t find a manual that tells me what number on the dial relates to 55 deg c water temp. They’re going to turn the dials down a bit and see if they are happy with non-scalding water and radiators.
This thing about condensing boilers running inefficiently because they’re not condensing: Question - when they are condensing should there be any visible steam coming from the flue ?

Depends on any energy recovery fitted on the exhaust - but you should have separate settings for heating and hot water temperatures. 
What’s the model?

It’s a Worcester Bosch 'Greenstar 25/30 S1’ I think it’s quite old and apparently the timer doesn’t work.

That can be replaced. 
I think this is from the guide for it 

There are a number of manuals depending on version and age 

Yes, there should be visible clouds of water vapour*, particularly on colder days.

That shows that what is being vented has had the heat reclaimed before being vented, and so is cool enough to quickly form those clouds in the open atmosphere.

It what is is being vented is not so visible then that’s probably because it’s too hot to cool quickly in the atmosphere and form clouds, so you are wasting that heat.

*Water vapour is sometimes called 'wet steam' particularly when it’s at close to 100C.
To get technical real steam at 100C is not visible at all, and steam can be at much higher temperatures than the 100C of boiling water, I'm sure that you may have heard of Superheated Steam, very useful in electricity generation among other uses.
(Arrgh, I used to do all that ‘properties of steam’ stuff in my first job after leaving school, mostly forgotten now).

Excellent !! Thankyou so much ​@Nukecad and ​@BPLightlog  - I’ll tell my friend to get a replacement timer.

You didn’t mention why you/your friend think that the timer isn’t working?

I do note that the one in your screenshot has the timing set for always on, so it should make no difference if the switch points to ‘On’ or to the clock symbol.

Those mechanical ones can be a bit tricky to work out and set, it’s pretty easy to get them 12 hours out if you aren’t paying attention to both the fingers and the numbers on the ring.
(I assume that photo wasn’t taken at five past one at night so the fingers/ring are aligned to the right 12 hours).

It also isn’t helped by the fact that on some of them pins-in is on, but on others it’s pins-out for on.

That one in your screenshot though has a handy little diagram showing pins-in for on, so it’s currently set for on all the time.

Thanks ​@Nukecad amazingly observant that’s v useful !! I have to admit I haven’t been over to my friend’s place so this is all done via photos and texts. I’m just taking his word for it re the clock not working. He said they just click the heating on and off using the thermostat !!! I’m going to go over soon and sort him out - trying the timer properly is now on the list.

He reports that the timer doesn’t go to round !

Probably broken then, but might just be stuck.

It appears to be a Worcester MT10 timer:

https://plumbsave.com/product/worcester-mt10-mechanical-time-switch-7716192036/

Some (newer?) versions don’t have fingers:
https://www.stuartplumbing.co.uk/worcester-mt10-mechanical-plugin-time-switch-7716192036/

Replacing one looks fairly simple, but taking the boiler casing off may be a bit too daunting for some people to tackle (if in doubt get a boiler engineer in to do it):
https://www.youtube.com/watch?v=f56ZjdxQKjw&ab_channel=BoilersToBathrooms

Hi

Not sure if I would agree with all the comments on boiler efficiency and setting.

With regards vapour: The cooler the boiler settings, the less water content in the flue and hence the less “steam” from the flue. The amount of steam visible is more likely to relate to the outside temperature.; the colder weather, the more steam.

Generally 50°C to 55°C for the water circuit is reasonable. Ours is set at 50°C and this is hot enough for washing, showers and baths.

Radiator circuit is set to a similar 50°C, however on really cold days we may need to increase this slightly so that rooms with smaller radiators can reach temperature.

Both these settings are more relevant if you have young children or elderly who are at risk of scalding/burning. (A friends son once had a fit and got trapped between radiator and bed causing burns - the hospital asked so many questions). To-day (-1°C outside) our lounge radiator is sitting at 46°C and has warmed the room in just over an hour.

Start lower and then work up in temperature if you have to.

BP

Thanks to both of you.. I found the timer on a well known suppliers website, then I found a debate on a diy forum re replacing said timer and whether it was a job for a gas safe engineer only. It seemed to depend on the model and what seal was between the casing and the components revealed under it. I expect they were offered a new timer at their latest service but declined as an unnecessary add on. 
Re the steam, there’s a short video of a flue at 70 v 35 deg showing steam v no steam. Not sure if the link can be included here but it’s from https://youtube.com/@tomasmcguinness?si=ZYjc_UY243pBdFyP which says to me lower is better ! 
My heat pump is running the rads at 42 deg at an outside temperature of -0.6 deg and house lovely and warm. 
My conversion with my friend about his boiler all started with him seeing a headline three figure sum from a well know energy supplier for a heat pump, and asking if it was possible !!