CH pressure gauge fluctuates between 0 and 1 bar?

[BAAZ]

Hello - First post so please bear with me...

We have a pressurised CH/DHW system with a non-combi boiler which was installed in 2005 replacing an old system. We didn't change all the pipes. Our flat is on the 5th floor of a block, and it is long (about 25 metres from one end to the other). The CH is pressurised and serves 10 radiators, 2 tall heated towel rails, and 2 plumbed-in plinth heaters in the kitchen. The DHW feeds a hot water tank and there is a hot water recirculation pump (looks like the central heating pump) which was installed due to the length of the flat.

Last week I noticed that the pressure gauge next to the expansion vessel was showing zero, and checked the flat below (which is empty) to find water marks on the ceiling. I opened the tap to refill the system and raise the pressure to about 1 bar, but it went back down to zero within an hour (system on). No evidence of water coming out of the expansion vessel overflow pipe outside, so I assumed there must be a leak in the radiators or pipes. Strangely, though, the heated towel rails (which are the highest point in the system - about 2 metres high) were still hot at the top.

I traced the source of the leak to the flexible pipes behind two plinth-heaters in the kitchen and called a plumber who has isolated them (they were on a separate circuit and we never used them anyway, so not worth the expense of replacing the leaky flexible pipes at this stage). They are not leaking any more. We set the pressure to about 1 bar after the repair.

Now, after a few days, I have noticed that the pressure gauge still reads around 1 bar when the CH/DHW is on, but drops back to zero (quite slowly) when the timer switches the CH/DHW off. This morning I switched them on manually (heating/hot water advance) and the pressure went back up to 1 bar within 5 minutes.

Any ideas? I assume that the fact that it has kept 1 bar of pressure for a few days means that there isn't a serious leak in the system. So why would it drop to zero when the timer switches the boiler off?

Any other tests I should do?

Thanks!

 

[AWheating]

its normal to have some movement on the gauge when the water in the system changes temp, this being said its sounds like alot to go from zero to one bar. I would suggest having your plumber to check the expansion vessel pressure and re pressurise the system to one bar when cold. If the expansion vessel is fine and you still get alot of difference from hot to cold pressures the vessel may be under sized for your system.