Modern condensing boilers are supposedly designed to modulate the heat
output. Am I correct in thinking that this modulation depends on the
temperature of the return water temperature and/or the setting on the
cylinder thermostat. My query is just how accurate and efficient is
this control process?
Is it a stepped process or truly linear.? For example, say its a
summer's day and the CH is not on so all the boiler has to do is keep
the hot water cylinder at the right temperature. You are all out that
day so there's no real demand for hot water. When the timer swithes
it on, the boiler presumably fires up and gradually brings the water
temperature back up to the temperature of the thermo stat on the
cylinder.
Can it modulate the gas consumption down progressivley within fine
limits eg 5% or is it a fairly rough comprimise eg down to 25% until
switching off when the thermostat limit is reached.
Incidentally, I have a Vaillant EcoMax Pro.

VT

In article
,
Vet Tech wrote:
Modern condensing boilers are supposedly designed to modulate the heat
output. Am I correct in thinking that this modulation depends on the
temperature of the return water temperature and/or the setting on the
cylinder thermostat. My query is just how accurate and efficient is
this control process?
Is it a stepped process or truly linear.? For example, say its a
summer's day and the CH is not on so all the boiler has to do is keep
the hot water cylinder at the right temperature. You are all out that
day so there's no real demand for hot water. When the timer swithes
it on, the boiler presumably fires up and gradually brings the water
temperature back up to the temperature of the thermo stat on the
cylinder.
Can it modulate the gas consumption down progressivley within fine
limits eg 5% or is it a fairly rough comprimise eg down to 25% until
switching off when the thermostat limit is reached.
Incidentally, I have a Vaillant EcoMax Pro.

It should keep the boiler running at its highest efficiency until the
desired temperature is achieved then switch off.

--
*He's not dead - he's electroencephalographically challenged

Dave Plowman London SW
To e-mail, change noise into sound.

In message , "Dave Plowman (News)"
writes
In article
,
Vet Tech wrote:
Modern condensing boilers are supposedly designed to modulate the heat
output. Am I correct in thinking that this modulation depends on the
temperature of the return water temperature and/or the setting on the
cylinder thermostat. My query is just how accurate and efficient is
this control process?
Is it a stepped process or truly linear.? For example, say its a
summer's day and the CH is not on so all the boiler has to do is keep
the hot water cylinder at the right temperature. You are all out that
day so there's no real demand for hot water. When the timer swithes
it on, the boiler presumably fires up and gradually brings the water
temperature back up to the temperature of the thermo stat on the
cylinder.
Can it modulate the gas consumption down progressivley within fine
limits eg 5% or is it a fairly rough comprimise eg down to 25% until
switching off when the thermostat limit is reached.
Incidentally, I have a Vaillant EcoMax Pro.

It should keep the boiler running at its highest efficiency until the
desired temperature is achieved then switch off.

Well, no

Think of the hysteresis

Modulation is primarily to keep the hot water constant. Being now
"office bound" and not actually doing any testing myself anymore - I
don't know

Vaillant have used both methods in the past, I think the EcoMax is
stepped (crudely so, IIRC)

--
geoff

In article ,
geoff wrote:
In message , "Dave Plowman (News)"
writes
In article
,
Vet Tech wrote:
Modern condensing boilers are supposedly designed to modulate the heat
output. Am I correct in thinking that this modulation depends on the
temperature of the return water temperature and/or the setting on the
cylinder thermostat. My query is just how accurate and efficient is
this control process?
Is it a stepped process or truly linear.? For example, say its a
summer's day and the CH is not on so all the boiler has to do is keep
the hot water cylinder at the right temperature. You are all out that
day so there's no real demand for hot water. When the timer swithes
it on, the boiler presumably fires up and gradually brings the water
temperature back up to the temperature of the thermo stat on the
cylinder.
Can it modulate the gas consumption down progressivley within fine
limits eg 5% or is it a fairly rough comprimise eg down to 25% until
switching off when the thermostat limit is reached.
Incidentally, I have a Vaillant EcoMax Pro.

It should keep the boiler running at its highest efficiency until the
desired temperature is achieved then switch off.

Well, no

Think of the hysteresis

Modulation is primarily to keep the hot water constant. Being now
"office bound" and not actually doing any testing myself anymore - I
don't know

Vaillant have used both methods in the past, I think the EcoMax is
stepped (crudely so, IIRC)

I didn't think we were talking about a combi.

--
*One nice thing about egotists: they don't talk about other people.

Dave Plowman London SW
To e-mail, change noise into sound.

On 22 Feb, 09:10, Vet Tech wrote:
Modern condensing boilers are supposedly designed to modulate the heat
output. Am I correct in thinking that this modulation depends on the
temperature of the return water temperature and/or the setting on the
cylinder thermostat. My query is just how accurate and efficient is
this control process?
Is it a stepped process or truly linear.? For example, say its a
summer's day and the CH is not on so all the boiler has to do is keep
the hot water cylinder at the right temperature. You are all out that
day so there's no real demand for hot water. When the timer swithes
it on, the boiler presumably fires up and gradually brings the water
temperature back up to the temperature of the thermo stat on the
cylinder.
Can it modulate the gas consumption down progressivley within fine
limits eg 5% or is it a fairly rough comprimise eg down to 25% until
switching off when the thermostat limit is reached.
Incidentally, I have a Vaillant EcoMax Pro.

VT

I have a Vaillant ecoTEC+ 937, when it fires, the burner is on the
lowest that it can go it gradually ramps up to full power and when it
is approaching the set flow temperature it modulates all the way down,
you can tell tell by the noise and the pump speed which automatically
switches between speed 1 and 2. Turn the CH knob higher and it will
ramp up the output again until the set flow temperature is reached.

With Vaillant controls the modulation depends on the set room
temperature

In message , "Dave Plowman (News)"
writes
In article ,
geoff wrote:
In message , "Dave Plowman (News)"
writes
In article
,
Vet Tech wrote:
Modern condensing boilers are supposedly designed to modulate the heat
output. Am I correct in thinking that this modulation depends on the
temperature of the return water temperature and/or the setting on the
cylinder thermostat. My query is just how accurate and efficient is
this control process?
Is it a stepped process or truly linear.? For example, say its a
summer's day and the CH is not on so all the boiler has to do is keep
the hot water cylinder at the right temperature. You are all out that
day so there's no real demand for hot water. When the timer swithes
it on, the boiler presumably fires up and gradually brings the water
temperature back up to the temperature of the thermo stat on the
cylinder.
Can it modulate the gas consumption down progressivley within fine
limits eg 5% or is it a fairly rough comprimise eg down to 25% until
switching off when the thermostat limit is reached.
Incidentally, I have a Vaillant EcoMax Pro.

It should keep the boiler running at its highest efficiency until the
desired temperature is achieved then switch off.

Well, no

Think of the hysteresis

Modulation is primarily to keep the hot water constant. Being now
"office bound" and not actually doing any testing myself anymore - I
don't know

Vaillant have used both methods in the past, I think the EcoMax is
stepped (crudely so, IIRC)

I didn't think we were talking about a combi.

http://www.wholesaleheating.co.uk/vaillant-boilers.html


--
geoff

In article ,
geoff wrote:
In message , "Dave Plowman (News)"
writes
In article ,
geoff wrote:
In message , "Dave Plowman (News)"
writes
In article
,
Vet Tech wrote:
Modern condensing boilers are supposedly designed to modulate the
heat output. Am I correct in thinking that this modulation
depends on the temperature of the return water temperature and/or
the setting on the cylinder thermostat. My query is just how
accurate and efficient is this control process? Is it a stepped
process or truly linear.? For example, say its a summer's day and
the CH is not on so all the boiler has to do is keep the hot water
cylinder at the right temperature. You are all out that day so
there's no real demand for hot water. When the timer swithes it
on, the boiler presumably fires up and gradually brings the water
temperature back up to the temperature of the thermo stat on the
cylinder. Can it modulate the gas consumption down progressivley
within fine limits eg 5% or is it a fairly rough comprimise eg
down to 25% until switching off when the thermostat limit is
reached. Incidentally, I have a Vaillant EcoMax Pro.

It should keep the boiler running at its highest efficiency until
the desired temperature is achieved then switch off.

Well, no

Think of the hysteresis

Modulation is primarily to keep the hot water constant. Being now
"office bound" and not actually doing any testing myself anymore - I
don't know

Vaillant have used both methods in the past, I think the EcoMax is
stepped (crudely so, IIRC)

I didn't think we were talking about a combi.

http://www.wholesaleheating.co.uk/vaillant-boilers.html

The OP seems convinced he has a storage cylinder.

--
*If you can't see my mirrors, I'm doing my hair*

Dave Plowman London SW
To e-mail, change noise into sound.

I didn't think we were talking about a combi.

--

No, not a combi. It's atraditional system with a bl**dy big cylinder.
It was a direct replacement for an old Netaheat system.

VT

On Sun, 22 Feb 2009 01:10:20 -0800, Vet Tech wrote:

Modern condensing boilers are supposedly designed to modulate the heat
output. Am I correct in thinking that this modulation depends on the
temperature of the return water temperature and/or the setting on the
cylinder thermostat. My query is just how accurate and efficient is this
control process?
Is it a stepped process or truly linear.? For example, say its a
summer's day and the CH is not on so all the boiler has to do is keep
the hot water cylinder at the right temperature. You are all out that
day so there's no real demand for hot water. When the timer swithes it
on, the boiler presumably fires up and gradually brings the water
temperature back up to the temperature of the thermo stat on the
cylinder.
Can it modulate the gas consumption down progressivley within fine
limits eg 5% or is it a fairly rough comprimise eg down to 25% until
switching off when the thermostat limit is reached. Incidentally, I have
a Vaillant EcoMax Pro.

VT

The external controls are either on or off.
The boiler however can modulate over a large range about 4:1. This is
truly linear, and is done by changing the speed of the premix fan.

The Vaillant is not as good as some models. Mainly all the models that
are 31kW or less are the same model. The only difference is how fast the
control firmware will allow the fan to run. So on the 31kW the fan can go
from 150-600 rpm but the top speed of the fan for the lesser models is
less and the depth of modulation is reduced. Also the max power in
heating mode is reduced further so that the max heating power of the 824
is only 19kW, but the minimum is still the same.

The fan can't go any slower as there is a minimum gas rate below which
instability of the flame might occur. If the boiler needs to output less
than ~8kW then it has to cut right out.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

On 22 Feb, 23:15, Ed Sirett wrote:

The fan can't go any slower as there is a minimum gas rate below which
instability of the flame might occur. If the boiler needs to output less
than ~8kW then it has to cut right out.

Much as I'd like to, I've not seen it cut out completely yet. The
flame 'icon' in the LCD display reduces in size to about half but it
still sounds as though the burner is still producing heat. Or might
it just be the fan on its own?
Given that the pump over-run would continue for 5 minutes after the
flame shut down, then there would inevitably be a modest reduction in
the return water temperature which in turn would fire up the burner
again. Hence causing a continuous loop. Is this a valid scenario?

Incidentally its an EcoMax Pro 18E which appears to be discontinued
now. It had the circuit board and the drain tank replaced replaced
after a year. Apart from that it's been OK
VT

On Tue, 24 Feb 2009 00:22:03 -0800, Vet Tech wrote:

On 22 Feb, 23:15, Ed Sirett wrote:

The fan can't go any slower as there is a minimum gas rate below which
instability of the flame might occur. If the boiler needs to output
less than ~8kW then it has to cut right out.

Much as I'd like to, I've not seen it cut out completely yet. The flame
'icon' in the LCD display reduces in size to about half but it still
sounds as though the burner is still producing heat. Or might it just
be the fan on its own?
Given that the pump over-run would continue for 5 minutes after the
flame shut down, then there would inevitably be a modest reduction in
the return water temperature which in turn would fire up the burner
again. Hence causing a continuous loop. Is this a valid scenario?

Incidentally its an EcoMax Pro 18E which appears to be discontinued now.
It had the circuit board and the drain tank replaced replaced after a
year. Apart from that it's been OK VT

What does parameter d.33 say?




--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html