Worcester oil fired boiler not cutting out therefore overheating

[eileen54]

My 7 year old oil fired boiler isn't cutting out and is therefore overheating the radiators. i have had a new thermostat fitted which worked for a few days but the problem has started again. Any ideas on what the problem could be?

 

[dontknowitall]

Have you a frost thermostat?

 

[eileen54]

I haven,t got a clue. The boiler is outside so I would hope it has a frost thermostat. At my wits end. Had engineer out last week and he changed thermostat but as it was still overheating, he turned boiler temp down to just under 1.

 

[SimonG]

Get him back to sort it out.

In the meantime what sort of boiler is it?

 

[eileen54]

It's a Worcester. He charged me £70.

 

[Bunker]

Are all your rads getting hot? Downstairs too?

(Question to the fellas: Will a frost stat engage the circulating pump too?)

Id be looking at a zone valve being stuck open but boiler should still cut out on the limit stat.

 

[alexmurchison]

regardless of stuck valves, the boiler shoild shut down if an overheat occurs on the high limit stat, which is set between 100 +110 degrees C. the boiler temp is regulated via the dial which you state he has turned down to under one. if it is still overheating, and he has checked the stats etc, may be control box , but this could be tested, hard to say without been there, but certainly control box, or around that area. If this was faulty it could quite possibly keep the burner running even when its been told to switch off.

 

[dontknowitall]

Frost stat should engage the pump or else the water won't travel around the system to warm the frost protected area.

 

[alexmurchison]

sorry, yes frost stat will activate pump on demand. as long as there is a pipe stat, this will cut the circuit and switch boiler off, if no pipe stat is fitted, the boiler will not shut down till limit stat is reached, if like you say the boiler is 7 year old,you can`t start questioning the way its fitted if its worked all these years, unless someone has tinkered with it. Outside worcester boilers have the frost stat fitted internally as standard, and require the switched and common live to work them. I have never had an issue with a frost stat packing up,so im not sure what the consequences would be, as frost stat is designed to overide all other controls

 

[Bunker]

but certainly control box, or around that area. If this was faulty it could quite possibly keep the burner running even when its been told to switch off.

not sure i get that. If there is no demand the control box won't get a live unless there is a fault on a control valve or as said above, the frost stat. Yes the limit stat should knock it off or very least the overheat stat (if there is one). Strange one this, maybe the boiler isn't overheating atall, symptoms arnt clear.

 

[alexmurchison]

not sure i get that. If there is no demand the control box won't get a live unless there is a fault on a control valve or as said above, the frost stat. Yes the limit stat should knock it off or very least the overheat stat (if there is one). Strange one this, maybe the boiler isn't overheating atall, symptoms arnt clear.

I stand corrected, quite true !
Eileen54 what is the boiler exactly doing ! is the pump running ? sorry, i know if you have little experience, these questions may not help ! when you say over haeting the radiators, can you explain you thinking this ? are they hotter than normal ?? your guy wants to check if stat is working, and that boiler does click off.

 

[lame plumber]

had same complaint recently on a gas boiler in boiler house, lady custard had turned it up as the temp dial was visible as it was cold in the house, boiler was running continuosly at 21'c, !!, proved it worked tho.

 

[kimbo]

It could be a faulty stat that was fitted and the limit stat could have gone faulty ages ago. I think but not sure that the worcesters have a high limit stat and an overheat stat and a control stat and if it was a combi there is a tank stat on toip of that. I would guess there may be more than one stat gone in which case rather than messing about with returns and how cheap the stats are I would change all three which would be cheaper than having a second call out in case the you got it wrong the first time.

 

[SimonG]

It could be a faulty stat that was fitted and the limit stat could have gone faulty ages ago. I think but not sure that the worcesters have a high limit stat and an overheat stat and a control stat and if it was a combi there is a tank stat on toip of that. I would guess there may be more than one stat gone in which case rather than messing about with returns and how cheap the stats are I would change all three which would be cheaper than having a second call out in case the you got it wrong the first time.

Aye the worcesters have the three, the overheat stat is self resetting and the high limit a manual reset.

 

[Best]

I wonder if it is going to the self setting stat which I think is just over 80 degrees?
I saw this with a STD eff. Worcester that had a faulty control stat, but when it was replaced the boiler was even hotter! Second new stat still was too hot & when I checked it from cold on lowest setting (1), temp was 65 when first off & a couple minutes later restarted & went up to over 80, turning off only on self setting overheat stat!

 

[kimbo]

High limit stat is 100deg and overheat stat is 110deg

 

[Best]

High limit stat is 100deg and overheat stat is 110deg

Edit :-
You are correct Kimbo, MIs of the boilers I am thinking of state same - 100 for H/L stat & 110 for O/H stat & the control stat has max of 82deg.
Perhaps I imagined it! Lol! :smile: But def had a test on a self setting stat that cut out at slightly >80deg.