What is the correct heating cycle for an oil boiler?

1. starting from a point when all calls for heat are OFF, and the flow
and return pipes have cooled:

2. A call for heat comes ON resulting in the flow pipe temperature
ramping up to the boiler limit, which turns off the boiler firing.

3. Now what should happen? SFAIUI there are 2 possibilities

- either the flow pipe drops to the lower boiler limit at which point
the boiler refires & the heating cycle resumes.

- or the ch control system senses the boiler is OFF; waits a short
time, then forces the boiler to refire, giving much more of saw tooth
pattern.

Apols if that is not very clear. Alternately can anyone please point
to a typical timing diagram? Being able to work out the whys and
wherefors of a diagram would probably clear up my queries.


TIA

"jim" wrote in message
...
What is the correct heating cycle for an oil boiler?

1. starting from a point when all calls for heat are OFF, and the flow
and return pipes have cooled:

2. A call for heat comes ON resulting in the flow pipe temperature
ramping up to the boiler limit, which turns off the boiler firing.

3. Now what should happen? SFAIUI there are 2 possibilities

- either the flow pipe drops to the lower boiler limit at which point
the boiler refires & the heating cycle resumes.

- or the ch control system senses the boiler is OFF; waits a short
time, then forces the boiler to refire, giving much more of saw tooth
pattern.

Apols if that is not very clear. Alternately can anyone please point
to a typical timing diagram? Being able to work out the whys and
wherefors of a diagram would probably clear up my queries.


TIA

Im can only answer for my oil system which is a pressure jet Stanley, the
call for heat is controlled by the temperature of the outlet of the boiler,
Call for heat burner fires up until correct water temp. is reached at
outlet of boiler, burner is then switched off until temp. drops, if it is
heating HW only, the length of time between firings is longer than if the
CH is running (obviously),
There is also a CH pump cut out if the temperature falls below 40deg IIRC to
prevent condensation in the boiler.
I have installed a solid fuel converted to oil fired Stanley and now have
installed a proper oil fired Stanley, so have been intimate with the
operation of both (and next door neighbours oil fired combi!!)

I will try and find the installation manual for the Stanley, I have it on
pdf somewhere in the depths of this PC.

Des

Dieseldes wrote:

"jim" wrote in message
...
What is the correct heating cycle for an oil boiler?

1. starting from a point when all calls for heat are OFF, and the flow
and return pipes have cooled:

2. A call for heat comes ON resulting in the flow pipe temperature
ramping up to the boiler limit, which turns off the boiler firing.

3. Now what should happen? SFAIUI there are 2 possibilities

- either the flow pipe drops to the lower boiler limit at which point
the boiler refires & the heating cycle resumes.

- or the ch control system senses the boiler is OFF; waits a short
time, then forces the boiler to refire, giving much more of saw tooth
pattern.

Apols if that is not very clear. Alternately can anyone please point
to a typical timing diagram? Being able to work out the whys and
wherefors of a diagram would probably clear up my queries.


TIA

Im can only answer for my oil system which is a pressure jet Stanley, the
call for heat is controlled by the temperature of the outlet of the boiler,
Call for heat burner fires up until correct water temp. is reached at
outlet of boiler, burner is then switched off until temp. drops, if it is
heating HW only, the length of time between firings is longer than if the
CH is running (obviously),
There is also a CH pump cut out if the temperature falls below 40deg IIRC to
prevent condensation in the boiler.
I have installed a solid fuel converted to oil fired Stanley and now have
installed a proper oil fired Stanley, so have been intimate with the
operation of both (and next door neighbours oil fired combi!!)

I will try and find the installation manual for the Stanley, I have it on
pdf somewhere in the depths of this PC.

Des

I agree with Des on this. If your boiler is straightforward you will
have two thermostats. One will be a high-limit safety stat designed
to protect from other control failures, probably fixed at 90 degrees.
The other will be the operating stat and you will probably have a
control on the front panel to set its operating point.
The boiler will come on and off depending on whether the *return*
temperature is above or below your set point allowing for the
hysterisis of the sensor. There will possibly be a small time delay
to prevent it refiring too soon after switching off and there will
almost certainly be a purge cycle at the beginning of the heat cycle
to prevent it booming as gasses in the boiler ignite in an
uncontrolled manner.

"Calvin" wrote in message
...
Dieseldes wrote:

"jim" wrote in message
...
What is the correct heating cycle for an oil boiler?

1. starting from a point when all calls for heat are OFF, and the flow
and return pipes have cooled:

2. A call for heat comes ON resulting in the flow pipe temperature
ramping up to the boiler limit, which turns off the boiler firing.

3. Now what should happen? SFAIUI there are 2 possibilities

- either the flow pipe drops to the lower boiler limit at which point
the boiler refires & the heating cycle resumes.

- or the ch control system senses the boiler is OFF; waits a short
time, then forces the boiler to refire, giving much more of saw tooth
pattern.


My boiler(s) fire if

a) The programmer supplies power.
b) The boiler temperature is below the adjustable limit, set using the
control knob.

There is no control system to sense that the boiler has been off and cause a
refire.

Apols if that is not very clear. Alternately can anyone please point
to a typical timing diagram? Being able to work out the whys and
wherefors of a diagram would probably clear up my queries.


TIA

Im can only answer for my oil system which is a pressure jet Stanley, the
call for heat is controlled by the temperature of the outlet of the
boiler,
Call for heat burner fires up until correct water temp. is reached at
outlet of boiler, burner is then switched off until temp. drops, if it
is
heating HW only, the length of time between firings is longer than if
the
CH is running (obviously),
There is also a CH pump cut out if the temperature falls below 40deg IIRC
to
prevent condensation in the boiler.
I have installed a solid fuel converted to oil fired Stanley and now have
installed a proper oil fired Stanley, so have been intimate with the
operation of both (and next door neighbours oil fired combi!!)

I will try and find the installation manual for the Stanley, I have it on
pdf somewhere in the depths of this PC.

Des

I agree with Des on this. If your boiler is straightforward you will
have two thermostats. One will be a high-limit safety stat designed
to protect from other control failures, probably fixed at 90 degrees.
The other will be the operating stat and you will probably have a
control on the front panel to set its operating point.
The boiler will come on and off depending on whether the *return*
temperature is above or below your set point allowing for the
hysterisis of the sensor. There will possibly be a small time delay
to prevent it refiring too soon after switching off and there will
almost certainly be a purge cycle at the beginning of the heat cycle
to prevent it booming as gasses in the boiler ignite in an
uncontrolled manner.



On the boilers that I have had it is the boiler temperature(s) rather that
the return temperature that is monitored.
(Though clearly the return temperaure is a factor in this.)

Most of the on/off cycling of my boiler is triggered by my programmable
thermostat.

The jet size is chosen to match the boiler output to the ability of the
radiators to give off heat.

--
Michael Chare