Boiler function question

[pma]

An easy one I hope!!

My view is...
When a boiler reaches its own inernal temperature limit (set by the burner potentiometer?- comments welcome), the boiler shuts down even if the room stat or cylinder stat are calling for heat. The pump continues to circulate water and when the temperature drops the Boiler stat (NTC sensor?) will automatically allow the boile to fire up again.

Is this correct?
Any other comments welcome. I'm tring to get fully familiar with boiler operation.

 

[baxpoti]

When a boiler reaches its own inernal temperature limit (set by the burner potentiometer?- comments welcome), the boiler shuts down even if the room stat or cylinder stat are calling for heat. The pump continues to circulate water and when the temperature drops the Boiler stat (NTC sensor?) will automatically allow the boile to fire up again.

Is this correct?

yes.... boiler 'stats' vary from 25 deg to 82 deg!

Any other comments welcome. I'm tring to get fully familiar with boiler operation.

Refer to manufacturers instruction booklet read cover to cover, you'll be as good as Agile (nearly)

 

[pma]

Thanks,

I have read from cover to cover, but these manuals always seem to omit the bit of info I specifically need.

So, just to clarify, should he boiler cut in and out according to its own internal temp regardless of calling from other system stats?

 

[ChrisR]

No... it won't light unless there's an external demand.
Then it lights if it isn't hot enough.

Boilers do vary though.

 

[pma]

Sorry, as usual I haven't explained myself well.

Assuming there is constant demand for heat from external stats, Boiler can cut in and out accoring to internal stat setting. (to protect from overheat?). Is this normal?

Thanks.

 

[EliteHeat]

Yes, but why would there be a constant demand? close the windows!

 

[ChrisR]

(to protect from overheat?).

No (aargh!!). The boiler stat may be marked say 1 to 6, which represents perhaps 55 to 82º. That's how hot the rads get. In spring/autumn the lower end would be better as it avoids temperature overshoot in the house. Though the HW cylinder would take longer to heat up.

(to protect from overheat?). there's another thermostat these days, the High Limit stat. These cut out at 90 - 100 and you have to press a button to reset them and get the boiler back on.

Not all boilers are exactly like that - do you have one in mind?

 

[pma]

I'm just trying to get to grips with the one I have and understand why it behaves as it does. Assuming there is calling for heat (both HW and CH), the boilr will cut out very quickly if HW only, much longer if CH or CH+HW.
I have Yplan system and pump is set to speed 3.

I'm puzzled!!!!

 

[ChrisR]

Well if you told us what you have...!
Remember you may have a 30kW boiler and a heat exchanger in the HW cylinder only capable of dumping 3kW - or less when the water's hot.

 

[stem]

You are right. The boiler thermostat regulates the temperature of the hot water leaving the boiler by switching the gas on and off automatically.

How often it does this depends on the temperature of the water comming into the boiler, the cooler this is the longer the boiler will fire to get it back to the required temperature.

 

[pma]

Sorry!
Boiler: Ideal Classic NF60 (18kW max)
Cylinder: Albion Thermal store, 160 Litre capacity. (using heat exchanger coil in tank)
There is a definate heating water temp difference in/out of tank.

Had this system in use for approx 4 years, provides great hot water (nothing but praise for it), but what I think has been another issue with the boiler has highlighted this cutting out timing anomoly.

 

[stevesey]

Baring a few differences in terminology (overheat thermostat vs bolier thermostat etc) you seem to have understtod what is going on. How about some details on the "other issue"? People may be able to help.

 

[pma]

The first issue was the boiler cutting out and not firing up again unless the boiler was swichted off and back on again.
My diagnosis for this is the PCB?
The second issue was that when HW was on on its own, the boiler would cut out very quickly. Checked wiring and system components, all appears ok! but this behaviour has bemused me.

Maybe it has alway done it? But only when the boiler starting playing up by not automatically firing up after cutting out, that the situation has become apparent?

This was why I asked about the internal thermostats controlling the boiler and how the boiler reacts to water temp. It may be that under normal operating conditions the boiler will happily cut in and out if the boiler stat so dictates.

What do you reckon?