Boiler cuts out

[trincomalee]

We have a Worcester Bosch Highflow 400 about 9 years old.
It cuts out every other day so needs pressing the restart button after I refill with water from the mains connection. This gets the pressure back up. I think it cuts out when pressure has dropped to about 15psi (1bar) so I refill till its 35psi (just over 2bar).
Sometimes water comes out the vent / overflow? pipe outside after refilling and sometimes the pressure shoots up to 3 bar.
Anyone have an idea of the problem?

 

[g20]

does pressure rise only when you turn the boiler on? or is it constantly rising?

 

[trincomalee]

Pressure drops about 0.2 bar when there is a demand for hot water (i.e. boiler comes on) and then when demand stops and boiler stops heating it goes back up the 2 bar it 'lost'.
The pressure increase events are rare.
Pressure not constantly rising.

 

[g20]

get a footpump and put it on your expansion vessel, it should be around 1.5bar, pump it up if lower

 

[trincomalee]

Thanks for suggestion! Pressure was at 1.3bar so have pumped to 1.5.
I guess that the difference of 0.2 below correct level may not be of significance? But its worth a check and set at correct level.

 

[Agile]

You can only repressurise the expansion vessel when the system water pressure is at zero. It should be set to 0.9 Bar.

The system pressure should then be set to 1.5 Bar.

Tony

 

[trincomalee]

Hi Agile,
How do I reduce the sytem water pressure to zero?
Setting the expansion vessel to 0.9bar I can do and also I assume repressurising the system via the inlet cold water is easy too.

 

[trincomalee]

Tony /agile, thanks for your suggestions by the way! It all helps.

 

[Agile]

Whilst still pressurised push the pin in the air valve to check that air and NOT water comes out!

Bleed about a litre of water from a bleed screw until the pressure falls to zero and then LEAVE it open as you repressurise to 0.9 Bar but expect more water may come out as you presurise. When youhave finished recheck the system presure is still zero.

Then close bleed screw and repressurise to about 1.5 Bar.

Tony

 

[trincomalee]

Tony,
All done as suggested. I guess I run it and see what happens now? System pressure would not go to exactly zero even with bleed valve completely out but that might be the pressure gauge not accurate. About 3litres of water eventually came out after repressurising the expansion vessel to 0.9bar (only about 1litre before that).
System now set at 1.5 and exp vessel at 0.9.
Thanks! Lets see if it runs ok for the next few days. Unless you have other suggestions for checking of course!

 

[gigz]

Keep an eye on the pressure relief discharge pipe, it could need replacing if it still drips

 

[trincomalee]

Thanks Gigz and Tony!
I'll see how it goes over the next few days.
Nick

 

[trincomalee]

Hi All,
The boiler ran successfully for 3 days before cutting out this morning(longer than usual). The system water pressure had dropped by 0.3bar to about 1.2bar. I topped up with mains water to return to 1.5bar fired up and all ok for now.
The pressure had been a constant 1.5 for 2.5 days prior to this.
Any ideas what might be causing the pressure loss and subsequent cut out?

 

[Agile]

You can only compare the pressure when the system is cold as expansion causes an increase of aboiut 0.3 Bar when hot.

Have you been monitoring the pressure relief valve outlet?

They sometimes drip but reaseal after a few days. If it continued leaking after a week or two then it will have to be replaced.

If you know how to "click" them a few times that sometimes helps to reseal.

Those 3 litres of water which came out have now been replaced with air to adsorb expansion.

Tony

 

[trincomalee]

No dripping from the outside pressure relief pipe (small copper pipe near ground level).
I don't know how to 'click' it but I know its the red knob on the left with '3 bar' written on it is the pressure relief valve.
The 3 litres that came out I assumed was replaced when I added more mains water? Maybe this was wrong and I should somehow let air do it?. (The plumber who fitted the boiler added a mains connection with a stop valve so it could be topped up if necessary).