Grant Vortex 36 Combi low pressure

[DJB2]

No, this is not another 'system pressure low in my boiler how do I fix it query'.

I installed my Grant Vortex 36 Combi in the summer last year. At the same time, I replaced ALL the pipework and several radiators. I opted for barrier pipe (Hep2O). Apart from some minor teething problems at the start such as not realising that Hep2O connectors didn't work with chrome pipes (replaced with compression joints) and a pressure gauge which didn't work because the hand had become detached from the spindle, all has worked well. Indeed the boiler still works well.

Recently I've noticed a problem. The system pressure is low (around 0.5 bar at cold). This is just within Grant's recommended pressure (0.5-1 bar). The problem is that when I try to top it up (only needed once a month or so), I can't get the pressure to go above 0.6 bar. I turn the 2 taps in the filling loop and very little happens. I've checked that neither end is blocked and there is good flow from each side.

What could cause this?

When I first installed the boiler, I could relatively easily fill the boiler up to 1.5 bar so I don't think that the mains pressure is low. I've removed as much of the air from the system as I can. I don't think that there is a significant leak. I've checked under the floor for this.

Please help.

D.

 

[Hugh Jaleak]

Are you confident the pressure gauge is working properly?

 

[DJB2]

It might not be, specially given the problem I had at the time of installing but I think that its probably ok. The low pressure warning light flashes on when I switch it off (maybe it always does this?). The odd thing is that when try to top up the pressure, I can't hear any flow unless the pressure's really low (ie near zero).

I presume the only way to check the guage is to replace it?

D.

 

[DJB2]

More convinced about guage being faulty or at least calibration incorrect. Decided to depressurise system (heat exchanger pipework isolated by closing CH pump and CH return stopcocks) by fully opening PRV until no water came out. I then removed the clear plastic cover over gauge and removed pointer (which was barely attached anyway). I then re-attached pointer at zero position. I re-filled the system and removed air. Re-calibrated guage now moved rapidly up to 1.5 bar so I reduced pressure a bit with PRV.

I suppose that I should purchase new guage just to be certain.

D.