Boiler stat failure? how?

[Agile]

If the boiler power output is set to match the heating requirement then it would take a long time to start boiling because the rads would dissipate all of the boiler's heat output.

In fact in most cases it would never boil at all because there would be insufficient power to raise the system water to a high enough temperature. Most of the time water boils in Bournemouth at about 99° C

Tony

 

[steved101]

seco, as agile has just said (what i am trying to kind of say)! : the room stat takes the temp of the room, say at 21, and the water in the oipe at this time is about 80ish. and the boiler stat is slightly higher, say 85ish, so boiler stat temp never reached anyway, so even if it had failed, the room stat temp 21 in the room/80 in the pipes, would prevent the boiler stat temp being reached and cut out the switched lived power before it boiled/reached 100 and pumped over......

 

[bengasman]

So basically, if a boiler stat fails, it is more than likely that another system fault is present and needs looking in to?

When a boilerstat fails, it just fails; in itself it does not indicate something else failing, but it could reveal it.

don't you mean manual bypass too far closed??

Could be either come to think of it. Short distance of pipe and high flow will not dissipate heat of boiler at full blast if the bypass is fully open.
Bypass closed and blockage preventing flow will also have lacking dissipation.

 

[Agile]

I cannot see any clues to indicate if there is any boiler bypass fitted.

25-30 years ago it was rare to fit them even if two port valves were fitted because the thermal inertia of the cast iron heat exchanger did not cause any obvious problem ( until they became scaled up ).

Tony

 

[Agile]

seco, as agile has just said (what i am trying to kind of say)! : the room stat takes the temp of the room, say at 21, and the water in the oipe at this time is about 80ish. and the boiler stat is slightly higher, say 85ish, so boiler stat temp never reached anyway, so even if it had failed, the room stat temp 21 in the room/80 in the pipes, would prevent the boiler stat temp being reached and cut out the switched lived power before it boiled/reached 100 and pumped over......

In this case the boiler is probably seriously over powered, partly because that was common practice as gas was then cheap, and partly because the house probably did not have double glazing or proper loft insulation then.

That resulted in short cycling on the boiler stat, when working, and very inefficient use of gas. Furthermore if the boiler stat were to fail then the boiler would quickly boil the system water which fills the loft with condensation and causes damage to upstairs ceilings in not turned off quickly.

Tony

 

[doitall]

Ok tell me how a boiler being scaled up can cause a boiler stat to fail?? Yes the boiler may cycle on and off quicker and the water not get to temp, but the scale will not affect the stat's workings.

If a room stat is set to 21 as the norm (80 plus in the pipes), and the boiler stat a little higher as the norm, then if the boiler stat fails, the room stat will break the circuit/power to the boiler's switched live BEFORE the boiler stat temp is even reached.

If i am wrong here then please explain why and I will hold my hands up and apologise

The stat pocket is in the waterways of the boiler, if it is scaled up you will get a false reading in much the same way as a scaled immersion heater.

 

[doitall]

If the boiler power output is set to match the heating requirement then it would take a long time to start boiling because the rads would dissipate all of the boiler's heat output.

In fact in most cases it would never boil at all because there would be insufficient power to raise the system water to a high enough temperature. Most of the time water boils in Bournemouth at about 99° C

Tony

So you are saying you don't need a boiler stat.

Furthermore if the boiler stat were to fail then the boiler would quickly boil the system water which fills the loft with condensation and causes damage to upstairs ceilings in not turned off quickly.

Hang on a change of plan, we do need a stat

 

[Razor900]

Of course if the OP's neighbour had gravity circulation to the hot water and no cylinder stat the boilers internal thermostat would be the only thing stopping a very hot shower

 

[steved101]

Ok tell me how a boiler being scaled up can cause a boiler stat to fail?? Yes the boiler may cycle on and off quicker and the water not get to temp, but the scale will not affect the stat's workings.

If a room stat is set to 21 as the norm (80 plus in the pipes), and the boiler stat a little higher as the norm, then if the boiler stat fails, the room stat will break the circuit/power to the boiler's switched live BEFORE the boiler stat temp is even reached.

If i am wrong here then please explain why and I will hold my hands up and apologise

The stat pocket is in the waterways of the boiler, if it is scaled up you will get a false reading in much the same way as a scaled immersion heater.

they are not always in the waterways. but yes if scaled up would make false readings, but then again the symptom would be lower tempeartue water at your rads (most noticeably) and h/w not as hot either. and boiler cycling, not pumping over.

 

[namsag]

DIA ,Seco dont waste your time trying to explain to someone who has not got a scooby ie steve look at his previous posts , cant even understand the basics and a it dont come any more basic than a boiler stat gone.
As for Agile would he not be better discussing this in CC as its embarassing that a pro such as himself cannot even understand something a 1st year apprentice would have no trouble with

 

[doitall]

You're not very good at this are you Steved.

If the boiler is scaled up, you will get kettleing (localized boiling)

Of course not all stats are in the waterways, and the clamp on type replies on a good contact, making overheating more possible.

A scaled boiler would also give you poor circulation, causing the boiler to overheat, and increase the risk.

 

[steved101]

yes, so as my earlier post- other than a wrongly/higher set gas valve (pressure) - a boiler stat failure usually always means another fault is present in the system, as you say scaled up, etc

if the boiler was scaled, and overheated, then it is not a faulty boiler stat at fault is it..... and the stat would reach temp quicker and cut off the supply. hence crap heat output.

 

[doitall]

No Steved.

Stats do go wrong, which is why they change the rags for immersion heaters, they must have a thermal cut-out now.

Wrong 2, if you insulate the phile/pocket with scale then it takes longer for the stat to react, so the boiler temperature will be higher.

 

[steved101]

i'm sorry, i get it now. what you sare saying is: if the stat is in a wet pocket waterway and gets scaled up, then the water temp will rise due to this, higher than it should, and thus an open vent ejection as it reaches boiling point/boils.


most boiler stat failures (ie leading pumping over) are due to other system fault(s), ie scaled up heat ex...?



my first point was this, please explain as i am trying to understand !! - sya the stat has just failed, no scale, etc - how would it get to 100 and pump over, wouldn't the room stat break the circuit before boiler stat temp??

 

[doitall]

yes, so as my earlier post- other than a wrongly/higher set gas valve (pressure) - a boiler stat failure usually always means another fault is present in the system, as you say scaled up, etc

The gas valve is not related to the operation of the boiler stat.