Combi boiler- How water not that hot anymore

[Geordie Spark]

And THAT Chris, is why I don't waste too much of my time writing long and detailed replies on here anymore!!!

 

[chris murphy]

And THAT Chris, is why I don't waste too much of my time writing long and detailed replies on here anymore!!!

"Hello again Geordie Spark",

Although I had a bit of a `Moan` - because I only respond to very few Posts / Questions on the Forum relating to Heating - Plumbing & Gas I don`t really mind having to `go into detail` / write quite long messages - although as I type using only ONE Finger they do take quite a lot of Time !

BUT - If I was responding to the amount of Posts that You do I would be `Well Browned Off` [or other similar phrases] if I wrote loads of very lengthy replies and was NOT even replied to by the OP`s.


Regards,

Chris

 

[cobrauk]

No worries m8 no offense taken and yes you right they don't say thanks to the help they get sometimes, but that life

 

[chris murphy]

No worries m8 no offense taken and yes you right they don't say thanks to the help they get sometimes, but that life

"Thanks cobrauk",

The LAST thing that I want is to be accidentally / incorrectly perceived as being Sarcastic / Obnoxious to other Members on the Forum.

I live My life trying to be Polite and well mannered at all times unless it is not possible because of the attitude of others.

Regards,

Chris

 

[Deleted member 26818]

I got a bit lost reading the posts on this thread.
I don't know if it's been suggested or not but here goes.
Many combi's have an adjustable temperature setting for both tap water and for radiator water.
Have you tried raising the setting for the tap water temperature?

 

[chris murphy]

I got a bit lost reading the posts on this thread.
I don't know if it's been suggested or not but here goes.
Many combi's have an adjustable temperature setting for both tap water and for radiator water.
Have you tried raising the setting for the tap water temperature?

"Hello spinlondon",

The OP stated that He wanted the Hot Water from his Combi Boiler to be at the 60 Degree Setting that He had selected on the Combi Hot Water Temperature selector - I then replied to Him including these comments:


REGARDING HIS HOT WATER NOT BEING AS HOT DURING THE LAST FEW WEEKS AS PREVIOUSLY:


It is VERY likely that this is because the temperature of the Incoming Mains Water is MUCH lower at this time of Year - without even Testing My Mains Water I know from experience that it will not be much more than 3 or 4 Degrees Centigrade - possibly only 2 Degrees.

MOST Combi Boilers are only capable of raising the temperature of the Mains Water by 35 Degrees at a Flow Rate of either approximately 9 Litres per Minute for the Lower Input / Output Combi`s - OR 12 Litres per Minute for the Higher Input / Output Combi`s.

SO:

If the incoming Mains Water in early November was for example 8 to 10 Degrees [Guesstimate] and the Combi is only capable of raising the Water temperature by 35 Degrees - theoretically the Hot Water Temperature would be 43 to 45 Degrees - this is quite Hot and would require mixing with the Cold Mains Water at the Shower - hence a reasonable Flow Rate and acceptable Temperature.

NOW / Cold Autumn / Winter Days & Nights:

Mains Temperature = 2- 3 or 4 Degrees - Heated by 35 Degrees = 37 - 39 Degrees - This is a VAST difference in Hot Water Temperature for Showering purposes !

While still too Hot to use the Hot Water only - even a slight introduction of Cold Mains Water will cause the Shower Temperature to be VERY noticeable as `Not anywhere near as Hot as previously` - as seems to have occurred in the OP`s enquiry.


END OF QUOTE


The Hot Water Temperature Selector [I won`t call it a `Thermostat`] on a Combi will only govern the Hot Water Temperature at the designed Flow Rate up to a point - that point is usually a 35 Degree rise in temperature from the incoming Mains Water temperature.

When the incoming Mains Water temperature is only a few Degrees above freezing - 2, 3 or 4 Degrees Centigrade - the Hot Water will never be Hotter than approximately 37 to 39 Degrees Centigrade - in the Spring and Summer it would probably be between about 50 to 55 Degrees Centigrade - a Vast difference in Hot Water temperature from Summer to Winter.


Regards,

Chris - Heating Engineer - Registered Gas Engineer - Qualified Plumber

 

[Deleted member 26818]

I'm quite aware that the mains temperature drops during the winter months.
It's just that before I'd suggest reducing water pressure (which is something the water board do where I live anyway), I'd suggest adjusting the temperature control, as that's usually quite simple, and won't affect a dishwasher or washing machine fill rate.

 

[fetamy]

Combi boiler problems are common, but after a while water heating process gets slow. Water circulation in heating systems diverted to heat exchanger. This makes cold water to warm more quickly.

 

[chris murphy]

I'm quite aware that the mains temperature drops during the winter months.
It's just that before I'd suggest reducing water pressure (which is something the water board do where I live anyway), I'd suggest adjusting the temperature control, as that's usually quite simple, and won't affect a dishwasher or washing machine fill rate.

"Hello spinlondon",

I am sure that You are quite aware that the Mains Water Temperature drops in the Winter / Autumn.

BUT - You did not seem to be aware that the OP had already stated that He would like His Combi to produce 60 Degree Temperature Hot Water.

I was trying to be polite to You when I went to the extent of typing out what I had informed Him about that point - because I thought that you had not seen what He wrote about `Selecting 60 Degree Hot Water on the Combi`

Also - at NO point did I suggest reducing the Incoming Mains Water Flow Rate / Volume [Not pressure] - I informed the OP that He would have to reduce the Flow Rate through the Shower and therefor through the Combi Boiler allowing the Water to Heat up to a higher temperature for Showering.

I realise that this will not be something that He or other people in this situation are happy about - but there will be plenty of Homes where a Shower which is supplied by Hot Water from a Combi Boiler and Cold Water from the Mains cannot be used effectively during periods when the Incoming Mains Water temperature is very low.

As I am writing this reply to You - were You aware of the fact that MOST of the lower Gas Input / Output Combi Boilers can only raise the Temperature of the Incoming Mains Water by approximately 35 Degrees Centigrade at a Flow Rate of approximately 9 Litres - even at the Hottest Temperature Setting - ?

I think that You may not have read all of the Posts that were submitted about this enquiry before You responded.

Regards,

Chris

 

[Mark_Burgess]

Excuse my ignorance but, I thought that when 'one' turns the temp dial up on the combi boiler it then regulates the water flow rate to get to the temperature requirement.

Surely turning the mains pressure down or the isolators to the shower is not the answer, get back who ever fitted the boiler or a registered installer to have a look.

 

[Spark1979]

A combi does not regulation flow rate of water through the boiler it regulates the gas valve to adjust the burner pressure hence giving more or less heat to the flow passing through the heat exchanger. The temp dial controls the temp of the return pipe to the burner after having passed through the secondary heat exchanger. I have not fully read the post but has the OP checked his hot taps to see if they are 'hot' as it could be a case that the mixer is on its way out, as it seems unlikely to be the boiler as he states it's new, older boiler do have a problem with lime scale in the secondary heat exchanger, also has the installer checked that he has the minimum burner pressure as laid out in the MF as this has a massive effect on hot water temp.

 

[chris murphy]

Excuse my ignorance but, I thought that when 'one' turns the temp dial up on the combi boiler it then regulates the water flow rate to get to the temperature requirement.

Surely turning the mains pressure down or the isolators to the shower is not the answer, get back who ever fitted the boiler or a registered installer to have a look.

"Hello Mark Burgess",


As Darrenburton has described turning Up the Hot Water Temperature Selector does NOT regulate the Incoming Mains Water Flow through the Combi.

Unless there is a problem with the OP`s Combi Boiler it is doing exactly what I explained in My previous `Lengthy` Post regarding the fact that a `Normal` / Lower Gas Input / Output Combi Boiler can only raise the Temperature of the Incoming Mains Water by approximately 35 Degrees Centigrade for an approximate Flow Rate of 9 Litres per Minute - AT the Highest Hot Water Temperature Setting.


SO:

Late Autumn / Winter Mains Water Temperature approximately 2- 3 or 4 Degrees - 35 Degree Rise = approximately 37 to 39 Degrees Hot Water.

Mid Autumn Mains Water Temperature - probably ranging from 12 Degrees to 8 Degrees - 35 Degree rise = approximately ranging from 47 to 43 Degrees Hot Water.

Summer Mains Water Temperature approximately 20 Degrees - 35 Degree rise = approximately 55 Degrees Hot Water.



Because this issue of the Hot Water from a Combi Boiler being very noticeably less Hot in the late Autumn / Winter is well known to people who have Combi Boilers - And Heating Engineers / Gas Engineers like Myself and Geordie Spark - I /We have explained the above to Him.

And unless He decides from using the Hot Water for other purposes that there is definitely something wrong with the Combi Boiler`s Hot Water production - I would NOT recommend the OP to engage the services of a Heating Engineer to look at this - with the obvious Cost involved.

IF THE OP WAS AT ALL INTERESTED IN ANY OF MY / OUR ADVICE - WHICH DOES NOT LOOK TO BE THE CASE:

I would recommend that He obtains a Thermometer and checks the Temperatures of both the Incoming Mains Water and the Hot Water - with the Hot Water regulated at approximately 9 Litres per Minute [by using a Tap / 2 Litre Bottle and a Watch] - looking for what I have stated is the usual 35 Degree Temperature rise that can be achieved by the average Combi Boiler producing Hot Water at approximately 9 Litres per Minute.


IF the Hot Water Temperature at the 9 Litre per Minute Flow Rate is NOT at approximately a 35 Degree rise from the Incoming Mains Water Temperature - then it would be appropriate for a Heating Engineer to be examining the Combi.


IF You read My Posts on this matter you would see that at NO point did I advise the OP to regulate the Incoming Water Mains - OR to regulate the supplies to the Shower at the Shower Isolating Valves [If it even has isolating valves].

By regulating the Water Flow through the Shower I mean simply not having a `Full Flow` rate through the Shower using the Shower Mixer / Thermostatic Valve.

When the Hot Water Temperature was higher and the Mains Water Temperature was not as Cold the OP could obviously have a greater Flow Rate through the Shower - NOW this will have to be a much lower Flow Rate - no doubt VERY noticeable and irritating.


I hope that this clarifies what I have been stating.


Regards,


Chris - Heating Engineer - Plumber - Gas Engineer - Heating, Plumbing & Gas Contractor.


FOR ANY INTERESTED PERSON:

THE HOT WATER FLOW RATE FROM COMBI BOILERS THAT HAVE A LARGER GAS INPUT / OUTPUT TO WATER IS HIGHER - TYPICALLY APPROXIMATELY 12 LITRES PER MINUTE AT A 35 DEGREE TEMPERATURE RISE.

OR THEY CAN SUPPLY A HIGHER TEMPERATURE RISE AT APPROXIMATELY 9 LITRES PER MINUTE - WHICH NEGATES THE ISSUE OF THE COLDER MAINS WATER TEMPERATURE IN AUTUMN / WINTER.

 

[chris murphy]

A combi does not regulation flow rate of water through the boiler it regulates the gas valve to adjust the burner pressure hence giving more or less heat to the flow passing through the heat exchanger. The temp dial controls the temp of the return pipe to the burner after having passed through the secondary heat exchanger. I have not fully read the post but has the OP checked his hot taps to see if they are 'hot' as it could be a case that the mixer is on its way out, as it seems unlikely to be the boiler as he states it's new, older boiler do have a problem with lime scale in the secondary heat exchanger, also has the installer checked that he has the minimum burner pressure as laid out in the MF as this has a massive effect on hot water temp.

"Hello Darrenburton",

The OP asked about the Hot Water Temperature at His Shower because He has obviously noticed the change in Temperature of the Hot Water on His body - He will obviously have checked the Hot Water at Taps also - but even 37 to 39 Degree Water is still `Hot` to the Hands.

Because the Shower should be supplied with Hot Water from the Combi and Cold Water from the Mains Water - when the Hot Water is much less Hot at this time of Year and Cold Mains Water [which is now colder] is mixed with that the resulting Flow from the Shower can be MUCH less Hot than it has been at other times of the Year for a similar Flow Rate.

Not only is the Hot Water much less Hot - but the Cold Mains Water is much Colder - resulting is MUCH less `Hot` Shower Water at even a lower Flow Rate.

Your point about the Burner Pressure would be applicable for older Combi`s - BUT - NEW - High Efficiency - Condensing Boilers / Combi`s do NOT have Gas Valves where the Burner Pressure can be adjusted.


Regards,


Chris - Heating Engineer - Plumber - Gas Engineer - Heating, Plumbing & Gas Contractor.

 

[puddy]

I had problems when Warmfront wanted to fit a new oil boiler they wanted to fit a combi I said no house is too big then they wanted to fit a floor mounted boiler I said no replace like with like i.e. wall mounted then they wanted to fit the 12/18 instead of the 18/25. I told Warmfront to look on bosch website they said no have the boiler fitted outside no I said. Got what I wanted in the end. If you have more than one bathroom then a combi wont heat enough hot water.

 

[chris murphy]

I had problems when Warmfront wanted to fit a new oil boiler they wanted to fit a combi I said no house is too big then they wanted to fit a floor mounted boiler I said no replace like with like i.e. wall mounted then they wanted to fit the 12/18 instead of the 18/25. I told Warmfront to look on bosch website they said no have the boiler fitted outside no I said. Got what I wanted in the end. If you have more than one bathroom then a combi wont heat enough hot water.

"Hello puddy",


Well done for `researching` about your Boiler / Heating & Hot Water requirements and sticking to what You wanted.

There are various Combination Boilers that are advertised by the Manufacturers to be able to suppy `High Hot Water demand` properties - for example the Ravenheat CSI 150 - a `42 KW Combi` - the published Hot Water supply specifications are:

D.H.W. FLOW RATE 30 °C rise 20.1 l/min

D.H.W. FLOW RATE 35 °C rise 17.3 l/min

D.H.W. FLOW RATE 40 °C rise 15.1 l/min

These stated Temperature rises are from a 10°C Cold Mains inlet temperature.


BUT - the Hot Water outlet pipe from the Combi is still only a 15mm Pipe - so it would still NOT be suitable to run Hot Water to TWO Hot Water outlets / Taps / Showers - especially if they were any distance [pipework] from each other.



Regards,


Chris - Heating Engineer - Registered Gas Engineer.