Hot water getting too hot

[Robbyg]

Need advice please...
if I run my newish boiler at 75c for max efficiency it's great for the central heating but my hot water gets too hot. its painful to touch and sometimes the shower pump cavitates and I only get a trickle out of my power shower and funny noises from the pump.

I need to run it with the hot water cylinder stat in the low 40s to help prevent the cavitation.
I fitted a new cylinder stat today thinking the old one might have been the problem but set at 50 the water is still way too hot.
Stat turns boiler off fine.
The problem seems worse when I am using the heating. (Guess the cold water is colder in winter so I use higher mix of hot water for shower)
I checked the 3 way valve there is no leakage flow to hw in ch mode.

i suspect by the time the boiler has been able to heat the top 3/4 of the tank to click off the stat, the water at the top of the tank has reached more like 70c.
ive got around it by running the boiler at about 60 all the time.

Is there a way to resolve this so I can run at 75c but have a tank full of useable temperature hot water?

Thanks

 

[Masood]

Turn your cylinder stat even lower than 40, so when it reaches, say 20C, the top is only at 55/60? Or move it higher up the cylinder? Assuming that is the only cause, and the 3-port is definitely not passing...

 

[Howsie]

Out of interest, why is 75deg the optimum for efficiency?

 

[Robbyg]

Out of interest, why is 75deg the optimum for efficiency?

That's what my boiler installer told me and what I thought was general statement for modern condensing boilers, run them a their hottest setting.75 is maximum for my boiler.
I guess it maximises the rate of heat transfer into water tank / from radiator so minimises time boiler has to run?

I know I can turn the stat down but I don't really want half a tank of scorching water and half Luke warm, that's what I am trying to solve.

 

[Ch3nKo]

Turning cylinder stat down from 60-65 degrees Celsius to 40 would surely promote bad bacteria inside of your stored hot water?

 

[Mike Jackson]

That's what my boiler installer told me and what I thought was general statement for modern condensing boilers, run them a their hottest setting.75 is maximum for my boiler.
I guess it maximises the rate of heat transfer into water tank / from radiator so minimises time boiler has to run?

Boiler stat should be set lower to maximise the time the boiler is in condensing mode.

Set at maximum the pump over run will carry on for longer and will be dissipating the excess heat into the cylinder meaning the cylinder will probably be getting up towards 70.

 

[nysk2008]

as previously stated, where on the cylinder have you located the cylinder stat? have you fitted the new cylinder stat correctly and to MI'S?

 

[happyflyer]

That's what my boiler installer told me and what I thought was general statement for modern condensing boilers, run them a their hottest setting.75 is maximum for my boiler.
I guess it maximises the rate of heat transfer into water tank / from radiator so minimises time boiler has to run?

I know I can turn the stat down but I don't really want half a tank of scorching water and half Luke warm, that's what I am trying to solve.

Its all here,

Is your condensing boiler actually condensing? | YouGen Blog | YouGen, Renewable Energy Made Easy

 

[Best]

Where on the hot cylinder is the cylinder stat positioned & also, is it making good contact?
The cyl. stat would be best about 1/3 up from bottom of tank, IMO & not any lower.
The boiler should be heating the cylinder water through the coil from the top of cylinder down gradually & shouldn't heat the top to, say, 70 degrees while the lower part of cylinder is fairly cool (as the cooler water will rob the heat out of the coil).

 

[Robbyg]

Edited borderline, lol I did see the un edited version and I do understand, seems common advice on modern boilers ( i received from various places) is incorrect.
Interesting link re condensing or not, makes scientific reason to me, thanks.

i suspect mine does very little condensing in hot water mode, though it certainly produces a lot of condensate in the winter. The return flow will be much cooler then.

sounds like I have no option but to continue as was.

not worried about bacteria in tank, the water will only be in there a few hours usually and will always get up to 50+ anyway before use. Same applies for any cylinder I guess.

 

[dancinplumba]

Thank you croppie

 

[dancinplumba]

Difficult to get your type of install to condense heating the hw cylinder, but run boiler on reduced stat setting that you are happy with, maybe turn it up in winter

 

[Simon F]

:sweatdrop:..How long do you have the programme on for hot water???
I have mine for an hour in the morning and again at tea time..:ihih:

:smart:.Simple solution, :lightbulb:..have it on for less time..:deal:




PS ;- Welcome to the forum.

 

[garyplumb]

Is the immersion on?