New home, new problems with boiler

Erni3wi5e491

Hi All,

First time posting and hoping to get some answers.

I have been handy for years and happy to delve into all manner of DIY including fixing and replacing parts on many a boiler in my time (never anything gas related.)

So my new house has a Main boiler. It was working fine until i went away for work and now my wife says it works fine for hot water but not heating. So obviously thought the tempostat was maybe acting up. 

On the boiler its around 1bar cold and when you turn on the heating, it drops to 0bar and trips to 118... But then... it returns to 1bar and allows hot water again? Like in the passed with Baxi i've had it where if the pressure drops it needs refilling before working again, but this seems to just return to working for hot water.

So my question is is this a new thing where the circuits are completely isolated so even if the heating is completely buggered it will still leave pressure in the circuit to allow for hot water?

Thanks in advance.

WIAWSNB

Is it a combi?

This has a round analogue pressure gauge? And it shows a solid 1 bar - in the green - when not running? 

Erni3wi5e491

Hi Thanks for the reply.

Yes Combi, analog gauge shows 1bar when running with hot water the same with not running but when changing to heating circuit it drops to pretty much 0 and then faults on F118 then once faulted and heating turns off it then goes back to 1bar and continues to work if hot water is demanded

WIAWSNB

That is weird.
The only time I've seen a pressure drop on boiler startup was on a floor-standing Potterton, and put it down to the pump location being forward of the pressure gauge. In essence, when the pump fired up, it caused a drop in pressure in it's wake, especially as it was dragging the CH system water behind it.
It didn't drop to anything like zero, but would reach 0.6bar, which would make the boiler stop. 
I topped up the expansion vessel which helped, and tweaked the 'cold' pressure to 1.5 bar, and that worked.
So, the EV might be a contributor (a GasSafe task if within the boiler casing), but no harm in topping up the cold pressure to, say, 1.5bar to see if that helps.
I'd be astonished if it drops to zero from that.

daveyjp

1 bar is the lower end of what I'd be comfortable with, especially with a basic analogue needle indicator.

Up the pressure to an indicated 1.4, 1.5 bar and see how you go.

WIAWSNB

Also, depending on where the pump is located in that model in relation to the diverter valve, if the valve isn't opening properly, the 'suction' could be more dramatic.
But pure speculation.