Adjusting hot water flow rate when combi boiler ignites

[Michael Chare]

Is the hot water flow rate at which a combi boiler ignites something
that is normally adjustable?

Or do I just have to live with the fact that if I turn a hot water on a
small amount all I will get is cold water?


--
Michael Chare

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

[johnje...@gmail.com]

The water flow has to be sufficient to operate the flow detector but only be flowing at a rate whereby the heat (gas/oil) input can raise the temperature of the flowing water to the desired temperature. You cannae beat the laws of physics Captain - Mr Scott, chief engineer of the starship Enterprise.

[Michael Chare]

Yes, but is it likely that I can adjust the rate at which the flow
detector triggers? Ideally I would like hot water to come from a hot
tap even if the tap is turned on a small amount. Not an issue when
having a bath, but it would make it easier to wash dishes.

[David]

On Sat, 27 Feb 2016 10:40:20 +0000, Michael Chare wrote:

> On 27/02/2016 10:15, johnje...@gmail.com wrote:
>> The water flow has to be sufficient to operate the flow detector but
>> only be flowing at a rate whereby the heat (gas/oil) input can raise
>> the temperature of the flowing water to the desired temperature. You
>> cannae beat the laws of
> > physics Captain - Mr Scott, chief engineer of the starship
> > Enterprise.
>>
>>
> Yes, but is it likely that I can adjust the rate at which the flow
> detector triggers? Ideally I would like hot water to come from a hot
> tap even if the tap is turned on a small amount. Not an issue when
> having a bath, but it would make it easier to wash dishes.

My inexpert view is that there will be a flow rate which matches the
minimum output of the boiler and stops the water going above the selected
temperature.

Below that flow rate the boiler will fire up, detect an overheat and turn
the flame off again. This would probably be very inefficient and not
acceptable to the manufacturer.

Depends on how low the boiler can throttle the heat source, but I would
not (in my inexpert opinion) expect it to be adjustable.

It may be an issue of boiler sizing - if you had a smaller boiler then you
could heat a slower flow of hot water but might struggle to heat the house
and fill a bath or run a shower.

[Note: it is said to be cheaper in energy terms to wash dishes in a dish
washer than by using the hot tap. No idea how long it takes to cover the
initial cost of the dishwasher, though.]

Cheers

Dave R

--
Windows 8.1 on PCSpecialist box

[Andrew Gabriel]

In article <djdjur...@mid.individual.net>,

This is correct.
If your boiler has a minimum burner rate of, say, 6kW, and you turn
on the tap so it only dribbles, 6kW would result in boiling that
flow rate, so boiler can't run safely and meet your max setting.

In theory, if you turn the hot water temperature to max (not safe
if you have children/elderly or anyone else who is not going to
expect it to change), then the boiler could sustain a lower hot
water flow rate (with much hotter water), but I don't know that
any of then actually measure the rate and compare it with the
set water temperature to decide when to cut-in.

If your boiler has an option to keep a litre or two hot ready
for use, this might help your case, depending how the boiler
manages its small water store.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

[John Rumm]

On 27/02/2016 10:05, Michael Chare wrote:


> Is the hot water flow rate at which a combi boiler ignites something
> that is normally adjustable?

No often...

> Or do I just have to live with the fact that if I turn a hot water on a
> small amount all I will get is cold water?

On some combi's yes. The ones that store and maintain a small store of a
couple of litres of hot water will work better in this respect, since
they will deliver that, and will also fire to re-temper that in addition
to the normal pressure drop triggering of the simpler models.

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

[Michael Chare]

On 27/02/2016 15:28, John Rumm wrote:
> On 27/02/2016 10:05, Michael Chare wrote:
>
>
>> Is the hot water flow rate at which a combi boiler ignites something
>> that is normally adjustable?
>
> No often...
>
>> Or do I just have to live with the fact that if I turn a hot water on a
>> small amount all I will get is cold water?
>
> On some combi's yes. The ones that store and maintain a small store of a
> couple of litres of hot water will work better in this respect, since
> they will deliver that, and will also fire to re-temper that in addition
> to the normal pressure drop triggering of the simpler models.
>

Thanks, I suspect that I have the latter. It does have a hot water
thermostat and I when I turned this up to near maximum I did get hot
water even with a slow flow rate. It was at 3/4 max before!

[The Natural Philosopher]

On 27/02/16 18:01, Michael Chare wrote:
> On 27/02/2016 15:28, John Rumm wrote:
>> On 27/02/2016 10:05, Michael Chare wrote:
>>
>>
>>> Is the hot water flow rate at which a combi boiler ignites something
>>> that is normally adjustable?
>>
>> No often...
>>
>>> Or do I just have to live with the fact that if I turn a hot water on a
>>> small amount all I will get is cold water?
>>
>> On some combi's yes. The ones that store and maintain a small store of a
>> couple of litres of hot water will work better in this respect, since
>> they will deliver that, and will also fire to re-temper that in addition
>> to the normal pressure drop triggering of the simpler models.
>>
>
> Thanks, I suspect that I have the latter. It does have a hot water
> thermostat and I when I turned this up to near maximum I did get hot
> water even with a slow flow rate. It was at 3/4 max before!
>
>

All combis are utter shite.


--
How fortunate for governments that the people they administer don't think.

Adolf Hitler

[John Rumm]

On 27/02/2016 18:01, Michael Chare wrote:
> On 27/02/2016 15:28, John Rumm wrote:
>> On 27/02/2016 10:05, Michael Chare wrote:
>>
>>
>>> Is the hot water flow rate at which a combi boiler ignites something
>>> that is normally adjustable?
>>
>> No often...
>>
>>> Or do I just have to live with the fact that if I turn a hot water on a
>>> small amount all I will get is cold water?
>>
>> On some combi's yes. The ones that store and maintain a small store of a
>> couple of litres of hot water will work better in this respect, since
>> they will deliver that, and will also fire to re-temper that in addition
>> to the normal pressure drop triggering of the simpler models.
>>
>
> Thanks, I suspect that I have the latter. It does have a hot water
> thermostat and I when I turned this up to near maximum I did get hot
> water even with a slow flow rate. It was at 3/4 max before!

It sounds more likely that previously it knew you were using water, but
could not fire the main burner without exceeding the maximum water
temperature you had specified.

The ones with a small amount of stored water, can't easily avoid giving
you the hot water at low flow rates, since its just sat there waiting to
be drawn off. (the boiler will also fire periodically for a few seconds
every few hours to keep the store hot). Some allow this feature to be
turned on or off.

[John Rumm]

as is that claim.

[The Natural Philosopher]

On 27/02/16 21:39, John Rumm wrote:
> On 27/02/2016 19:01, The Natural Philosopher wrote:
>> On 27/02/16 18:01, Michael Chare wrote:
>>> On 27/02/2016 15:28, John Rumm wrote:
>>>> On 27/02/2016 10:05, Michael Chare wrote:
>>>>
>>>>
>>>>> Is the hot water flow rate at which a combi boiler ignites something
>>>>> that is normally adjustable?
>>>>
>>>> No often...
>>>>
>>>>> Or do I just have to live with the fact that if I turn a hot water
>>>>> on a
>>>>> small amount all I will get is cold water?
>>>>
>>>> On some combi's yes. The ones that store and maintain a small store
>>>> of a
>>>> couple of litres of hot water will work better in this respect, since
>>>> they will deliver that, and will also fire to re-temper that in
>>>> addition
>>>> to the normal pressure drop triggering of the simpler models.
>>>>
>>>
>>> Thanks, I suspect that I have the latter. It does have a hot water
>>> thermostat and I when I turned this up to near maximum I did get hot
>>> water even with a slow flow rate. It was at 3/4 max before!
>>>
>>>
>> All combis are utter shite.
>
> as is that claim.
>
>

I have never ever had satisfactory hot water from any combi. Period.



--
You can get much farther with a kind word and a gun than you can with a
kind word alone.

Al Capone

[Richard]

"The Natural Philosopher" wrote in message
news:natl5d$7cq$1...@news.albasani.net...

You haven't tried many then.

>Period.
That explains the mood swings!

[Dave Plowman (News)]

In article <djdjur...@mid.individual.net>,

David <wib...@btintenet.com> wrote:
> [Note: it is said to be cheaper in energy terms to wash dishes in a dish
> washer than by using the hot tap. No idea how long it takes to cover the
> initial cost of the dishwasher, though.]

And the cost of the expensive detergent. 30p a wash for some branded
products. Far more than any energy costs.

--
*I used to be a banker, but then I lost interest.*

Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.

[Dave Plowman (News)]

In article <j6GdnQMqTeETik_L...@brightview.co.uk>,

John Rumm <see.my.s...@nowhere.null> wrote:
> On 27/02/2016 19:01, The Natural Philosopher wrote:
> > On 27/02/16 18:01, Michael Chare wrote:
> >> On 27/02/2016 15:28, John Rumm wrote:
> >>> On 27/02/2016 10:05, Michael Chare wrote:
> >>>
> >>>
> >>>> Is the hot water flow rate at which a combi boiler ignites something
> >>>> that is normally adjustable?
> >>>
> >>> No often...
> >>>
> >>>> Or do I just have to live with the fact that if I turn a hot water on a
> >>>> small amount all I will get is cold water?
> >>>
> >>> On some combi's yes. The ones that store and maintain a small store of a
> >>> couple of litres of hot water will work better in this respect, since
> >>> they will deliver that, and will also fire to re-temper that in addition
> >>> to the normal pressure drop triggering of the simpler models.
> >>>
> >>
> >> Thanks, I suspect that I have the latter. It does have a hot water
> >> thermostat and I when I turned this up to near maximum I did get hot
> >> water even with a slow flow rate. It was at 3/4 max before!
> >>
> >>
> > All combis are utter shite.

> as is that claim.

It is Rees-Turnip, remember. Only black and white in his tiny world.

I prefer a storage system for my needs - and it already exists here
anyway. Others may have different needs and priorities.

--
*I'm really easy to get along with once people learn to worship me

[newshound]

On 2/27/2016 3:28 PM, John Rumm wrote:
> On 27/02/2016 10:05, Michael Chare wrote:
>
>
>> Is the hot water flow rate at which a combi boiler ignites something
>> that is normally adjustable?
>
> No often...
>
>> Or do I just have to live with the fact that if I turn a hot water on a
>> small amount all I will get is cold water?
>
> On some combi's yes. The ones that store and maintain a small store of a
> couple of litres of hot water will work better in this respect, since
> they will deliver that, and will also fire to re-temper that in addition
> to the normal pressure drop triggering of the simpler models.
>

I've had two in my (larger, old house with inconvenient pipe runs) and
neither were ever really satisfactory for DHW, even when new. I added a
separate, electrically heated supply for the kitchen sink, then an
electrically heated hot water cylinder for a shower. Problems solved
with the third boiler, a conventional system boiler heating the hot
water cylinder.

[Dave Plowman (News)]

In article <KYednWXm4INPZk_L...@brightview.co.uk>,

In my case both the boiler and storage tank are in the bathroom. So get
near instant hot water there. In the kitchen, it takes more time to run
hot. If I had a combi in the kitchen, I'd expect hot water quite quickly
but slower in the bathroom.

So basically how quickly you get hot water is going to depend on lots of
things.

--
*Whatever kind of look you were going for, you missed.

[Rod Speed]

Dave Plowman (News) <da...@davenoise.co.uk> wrote

> David <wib...@btintenet.com> wrote

>> [Note: it is said to be cheaper in energy terms to wash dishes
>> in a dish washer than by using the hot tap. No idea how long
>> it takes to cover the initial cost of the dishwasher, though.]

Not long if you buy it used at a garage sale.

> And the cost of the expensive detergent.
> 30p a wash for some branded products.

But nothing like that from Aldi etc.

[Rod Speed]

"Dave Plowman (News)" <da...@davenoise.co.uk> wrote in message
news:5559050...@davenoise.co.uk...

> In article <KYednWXm4INPZk_L...@brightview.co.uk>,
> newshound <news...@stevejqr.plus.com> wrote:
>> On 2/27/2016 3:28 PM, John Rumm wrote:
>> > On 27/02/2016 10:05, Michael Chare wrote:
>> >
>> >
>> >> Is the hot water flow rate at which a combi boiler ignites something
>> >> that is normally adjustable?
>> >
>> > No often...
>> >
>> >> Or do I just have to live with the fact that if I turn a hot water on
>> >> a small amount all I will get is cold water?
>> >
>> > On some combi's yes. The ones that store and maintain a small store of
>> > a couple of litres of hot water will work better in this respect,
>> > since they will deliver that, and will also fire to re-temper that in
>> > addition to the normal pressure drop triggering of the simpler models.
>> >
>> I've had two in my (larger, old house with inconvenient pipe runs) and
>> neither were ever really satisfactory for DHW, even when new. I added a
>> separate, electrically heated supply for the kitchen sink, then an
>> electrically heated hot water cylinder for a shower. Problems solved
>> with the third boiler, a conventional system boiler heating the hot
>> water cylinder.
>
> In my case both the boiler and storage tank are in the bathroom.

I don’t have a boiler, but the storage tank is in the bathroom/laundry.

> So get near instant hot water there. In the kitchen, it takes
> more time to run hot. If I had a combi in the kitchen, I'd
> expect hot water quite quickly but slower in the bathroom.

> So basically how quickly you get hot water
> is going to depend on lots of things.

And given that I hardly ever use hot water in the kitchen,
and use it at least once a day in the bathroom, it makes
a lot more sense to have the storage in the bathroom.

And what minimal waste heat leaks from it there is more
use in the bathroom in winter than in the kitchen too.

[ARW]

"Rod Speed" <rod.sp...@gmail.com> wrote in message
news:djgpro...@mid.individual.net...

And the dishes are cleaner.

--
Adam

[Fredxxx]

On 27/02/2016 19:01, The Natural Philosopher wrote:

Making such a wide ranging assertion says more about your blinkered view
of the world than you understand, or will ever have understood.

Combis are fine in many situation. They are compact, efficient in that
no water need be stored, and these days with modulating boilers have
sufficient flow for most needs, certainly greater than any electric shower.

I do suggest you rethink your absurd comment.

[John Rumm]

So based on that sample size of one, you are happy to extrapolate to the
every installation of every boiler?

[Rod Speed]

"ARW" <adamwa...@blueyonder.co.uk> wrote in message
news:navc8b$a05$1...@dont-email.me...

Yeah, vastly better than with hand washing.

[Michael Chare]

On 27/02/2016 21:38, John Rumm wrote:
> On 27/02/2016 18:01, Michael Chare wrote:
>> On 27/02/2016 15:28, John Rumm wrote:
>>> On 27/02/2016 10:05, Michael Chare wrote:
>>>
>>>
>>>> Is the hot water flow rate at which a combi boiler ignites something
>>>> that is normally adjustable?
>>>
>>> No often...
>>>
>>>> Or do I just have to live with the fact that if I turn a hot water on a
>>>> small amount all I will get is cold water?
>>>
>>> On some combi's yes. The ones that store and maintain a small store of a
>>> couple of litres of hot water will work better in this respect, since
>>> they will deliver that, and will also fire to re-temper that in addition
>>> to the normal pressure drop triggering of the simpler models.
>>>
>>
>> Thanks, I suspect that I have the latter. It does have a hot water
>> thermostat and I when I turned this up to near maximum I did get hot
>> water even with a slow flow rate. It was at 3/4 max before!
>
> It sounds more likely that previously it knew you were using water, but
> could not fire the main burner without exceeding the maximum water
> temperature you had specified.
>
> The ones with a small amount of stored water, can't easily avoid giving
> you the hot water at low flow rates, since its just sat there waiting to
> be drawn off. (the boiler will also fire periodically for a few seconds
> every few hours to keep the store hot).

Thanks, my suspicion is that the boiler is not working properly. I
really need to take the covers off and see if I can find anything with
my meter. Unfortunately the boiler is under a worktop which has to be
removed first.

[John Rumm]

I have experienced a few over the years... the first (when I was a kid)
was not a combi, but a multipoint. That replaced a electrically heated
cylinder. It was fairly crude and not passively powerful. You needed to
turn a tap on fairly hard to get it to fire at all, and when running it
could only deliver about 9 or so lpm of hot water. You had to learn to
not turn taps on too hard, or the temperature would fall. So it had its
limitations, but in one respect was a massive improvement on the system
it replaced, it meant there was hot water available all the time, which
was a big step forward. (the cylinder was manually controlled, and non
thermostatic - so got turned on twice a week to heat water on "bath
nights". It was also not lagged!)

The second was a combi made by Main. Slightly better than the multipoint
for maximum flow rate but in other respects similar. However that was a
*massive* step forward since it was the first time we had CH, and the
first time the house was properly warm in the winter.

First house I bought, had a stored hot water system heated from the CH
boiler. It was poorly implemented and not very good. Showers were
feeble, reheat times very slow. Bath filling was better, but not by
much. When I did a loft conversion on that place, it meant all the
stored water kit needed to go, so I fitted a 35kW modulating combi. That
was the best so far, it would do one excellent shower, or two ok showers
at a time. Bath filling was on par with the previous stored water system
but without the limitation of continuously running out of water.

This house had an even more crap gravity hot water system. Not enough
water, pressure, slow reheat - you name it, it failed doing it. That I
replaced with a mains pressure 210L unvented cylinder heated by a system
boiler. Certainly the best system yet, although three times the price of
a decent combi.

Others I have encountered include a modern combi in a small semi, with
one shower room only. Absolutely ideal - it meets every demand made of
it, and saves space and uses far less gas than the Ideal Mexico cast
iron lump it replaced. It meant the small bathroom could be adapted for
its elderly occupant with a walk in shower and lots of other easy access
facilities.

No system is perfect. but in the right circumstances, a combi can be the
best compromise.

[John Rumm]

Note that on the ones that do keep a small amount of water tempered,
there is often a configuration option to turn this capability off - so
just because the boiler supports it, does not mean its always used.

[Andrew]

On 27/02/2016 10:05, Michael Chare wrote:

> Is the hot water flow rate at which a combi boiler ignites something
> that is normally adjustable?
>
> Or do I just have to live with the fact that if I turn a hot water on a
> small amount all I will get is cold water?
>
>

Some makes have a setting that allows them to learn what your
requirements are and will fire up occasionally just to heat up the
primary circuit. Then when you want hot water the delay is shorter, but
it uses more gas.