Boiler cut off.

Eldi_Dos

I got up early a couple of Saturdays ago to find that the hot water tap in bathroom sink was about a quarter on and running cold.Think it could have been like this for up to three hours.

Later on when I got up found that no hot water was available from any taps and on checking boiler the digital display showed LPL (or similar) and the circular pressure gauge was at zero.
Checked radiators and elsewhere for leaks, non found, then using repressure lever pressurised the system, which it did instantly on the pressure gauge.Since then everything has been fine and gauge holding steady.

I presume a safety feature kicked in with the tap being left on for so long at a low output.
I wonder if someone could confirm this and explain the mechanism of how it works.

It is a WB Greenstar 30K boiler coming up for two year old.

ButterCheese

I've never heard of this happening but it does make sense with a newer boiler.  I would imagine there's no reason anyone would demand hot water for 3 hours so it may have sensed this and shut off.  I assume it would now know to do this if the heating was on constant though!

WIAWSNB

If the analogue pressure gauge needle was at zero, then that indicates a pressure loss, and is not an indication of a safety feature having kicked in - other than the boiler turning off due to this lack of pressure.

So, I suspect, if your boiler was supplying DHW for up to three hours, it may have overheated, the internal pressure then reached ~3bar, and this dumped the excess system water out the safety discharge pipe. Then your boiler would have shut down due to the lack of pressure. 

Ok, it shouldn't have done this, but hey. 

That's a pure guess. I can see no other connecting element.

Anyhoo, I presume you repressurised to around 1.2bar, and all is well - that reading remains pretty stable whether the boiler is running or off? 

Eldi_Dos

WIAWSNB said:

Anyhoo, I presume you repressurised to around 1.2bar, and all is well - that reading remains pretty stable whether the boiler is running or off? 

Yeah when I repressurised using the little blue lever on the pressure loop the needle on the circular gauge immediately returned to 1.25 bar where it has always sat.The speed that the needle returned to normal would indicate to me that no water had been dumped during intial cut off.

Edit: I mean no water below 1.25bar. I did check discharge pipe outside and could see no sign of discharge, although this could have been up to six hours after cut off occurred.

WIAWSNB

Eldi_Dos said:

WIAWSNB said:

Anyhoo, I presume you repressurised to around 1.2bar, and all is well - that reading remains pretty stable whether the boiler is running or off? 

Yeah when I repressurised using the little blue lever on the pressure loop the needle on the circular gauge immediately returned to 1.25 bar where it has always sat.The speed that the needle returned to normal would indicate to me that no water had been dumped during intial cut off.

Edit: I mean no water below 1.25bar. I did check discharge pipe outside and could see no sign of discharge, although this could have been up to six hours after cut off occurred.

Interesting.
As you say, with a genuine zero pressure, you'd expect a good few seconds worth of topping-up, accompanied by a suitable hiss of flowing water. 
I'm at loss.