W/B Greenstar Heatslave 25/32 (installed 2009)

[Terrym]

Hi, any advise would be welcomed.

My boiler has locked out, due, I believe to water overheating. Although the water in the boiler seems to be piping hot, the only water coming from the hot tap is cold. If I let the water cool down over time, the boiler resets ok, but when the water gets hot again the boiler locks out. Same thing again, no hot water comes from hot water tap. I’ve changed the hot water thermostat, but no difference. Any suggestion?
Terry

 

[SJB060685]

You say lockout, do you mean the burner is going to lockout? Is the heating working OK?

 

[Terrym]

Yes, boiler goes into lockout. Heating not working either.

 

[SJB060685]

Ok. Burner lockout is a problem related to the burner and not related to the temperature of water. I wouldn't go replacing anymore parts in the hope to rectify and advise you to call an engineer out. It could be a few things based on what you said above but hard to say where to start without being there.

 

[Terrym]

Ok. Burner lockout is a problem related to the burner and not related to the temperature of water. I wouldn't go replacing anymore parts in the hope to rectify and advise you to call an engineer out. It could be a few things based on what you said above but hard to say where to start without being there.

Sorry, I may have mislead you, but difficult to describe from my point of view. I can only explain that that the boiler reset pops out as soon as the temperature gets too hot. As stated before that at that point there is no hot water coming out of hot tap, but there appears to be plenty of really hot water stored in boiler. Then as mentioned boiler will not reset, but when left to cool down naturally it does reset and boiler runs, but only for a few minutes until the reset button pops out again. Again sorry, but don’t know how to explain it any better.

 

[SJB060685]

So your temperature limit stat pops out and you have to manually reset it correct? And which stat did you replace?

 

[SimonG]

Bleed the pump. Was the pressure low and you topped it up?

 

[Terrym]

So your temperature limit stat pops out and you have to manually reset it correct? And which stat did you replace?

Yes, that’s correct. I changed the hot water stat. Thanks for your patience.
Terry

 

[Terrym]

Bleed the pump. Was the pressure low and you topped it up?

Hi Simon, I haven’t adjusted the pressure, it currently reads around 1.5 bar.

 

[SJB060685]

As my friend Simon has said above, has anything changed/happened recently? Providing I'm looking at the right manual (several versions of this boiler over the years) then there is a series of thermostats in series before the manual reset thermostat. It's possible either the auto reset high limit stat is faulty or the manual reset overheat stat is faulty. I would want to be checking the temperature with a digital thermostat in the thermostat pockets.

 

[exedon2]

When you say you re set the boiler is it burner lock out you re set or the manual over heat on boiler? From memory there is also a manual over heat stat on hot water tank.

 

[Terrym]

As my friend Simon has said above, has anything changed/happened recently? Providing I'm looking at the right manual (several versions of this boiler over the years) then there is a series of thermostats in series before the manual reset thermostat. It's possible either the auto reset high limit stat is faulty or the manual reset overheat stat is faulty. I would want to be checking the temperature with a digital thermostat in the thermostat pockets.

I’m not being much help I’m afraid, but thinking back a few weeks ago I may have increased the pressure slightly, but can’t remember why. If there is air in the pump could this be the reason why there is no hot water coming out of the hot tap? Excuse my ignorance. If so can the pump be bled in situ, is the bleed screw accessible?

 

[Terrym]

When you say you re set the boiler is it burner lock out you re set or the manual over heat on boiler? From memory there is also a manual over heat stat on hot water tank.

Yes, it’s the manual overheat reset on the boiler.

 

[SJB060685]

If there is air in the pump this can and will cause an airlock and no circulation, this will cause the temperature in the primary exchanger to rise rapidly causing your problem. Do you have any hot water or heating before the stat locks out?

 

[Terrym]

If there is air in the pump this can and will cause an airlock and no circulation, this will cause the temperature in the primary exchanger to rise rapidly causing your problem. Do you have any hot water or heating before the stat locks out?

No, none.

 

[SJB060685]

So no hot water or heating? In that case I suspect the pump has either an airlock as already mentioned or the pump has failed.

 

[Terrym]

So no hot water or heating? In that case I suspect the pump has either an airlock as already mentioned or the pump has failed.

Sounds like the pump is running and if I touch it I can feel vibration. Certainly worth trying to bleed. Is it easy to get to the bleed screw in situ?

 

[SJB060685]

There will be a grub screw on the face of the pump you loosen and vent any air.

 

[Terrym]

There will be a grub screw on the face of the pump you loosen and vent any air.

Ok, I’ll have a look and give it a go. I’ll report back, but won’t be able to try for a little while. Thanks for everybody’s input so far.
Terry

 

[Terrym]

Ok, I’ll have a look and give it a go. I’ll report back, but won’t be able to try for a little while. Thanks for everybody’s input so far.
Terry

Bled the air out of the pump and bingo, problem solved. Thank you so much for everybody’s input. I am so chuffed, no need for another cold shower.!!!

 

[SimonG]

Badly designed boiler, pump on the top. They added an auto air vent by the pump later.

It's a common problem, even de pressurising the boiler to check the expansion vessel charge can cause it.