Any plumbers around who might be able to help?

[Bazzer]

I have a Worcester Bosch 38CDi with a linked unvented cyclinder, which is run off like a separate radiator and is used for a shower cabin. Long story short, I had to check a valve on a downstairs hot water tap. The cold water inlet is in an awkward position and I thought I had turned off the water supply, so I could remove the valve. I hadn't, but by the time I realised my mistake the boiler pressure was down to zero. The boiler was turned off at the mains and I turned my attention to the tap.
The tap was sorted and I came to refill the boiler but it isn't happening. The cold water inlet was turned back on and the isolating valve on the filling loop by the boiler turned on. The blue cold water inlet switch on the boiler was pulled down and initially water could be heard, then nothing. The gauge doesn't move and there remains no sound of water.
I have checked the other side of the flexible pipe on which the isolating valve sits and there is water. I have looked in the commissioning instructions and can't see what I am doing wrong. As it's BH tomorrow and with the virus still going around, can someone provide some advice please?
Edit: the boiler was fitted in November 2018 and was serviced in January. The unvented cylinder is also new having been fitted in February when its predecessor leaked.

 

[I like Skol]

I can't picture what you are describing here. The heating/radiator loop is seperate from your tap water supply, so working on one won't affect pressure in the other. What does this seperate unvented cyclinder do?
Sometimes on very large heating systems it is necessary to add in an additional pressurised expansion tank but that has nothing to do with the hot water tap supply.

 

[Bazzer]

The separate unvented cylinder goes only to a shower cabin because the heater is a combi and it reduces the pressure loss if someone turns on a hot tap when someone else is having a shower.
I am hoping in the last few minutes I have found the problem. Having visually gone over the water inlet system time and time again, in desperation I turned the boiler on. Immediately the pressure gauge sprung to life. Thankfully, only showing 1 bar and it now happily and properly tops up to the correct 1.5 bar. Hopefully it was just a valve, relay or similar which just got stuck.

 

[sleuthey]

Perhaps your mistaking something else for a filling loop. I have a 27cdi and you put a white key vertically upwards into the inbuilt filling loop, turn the key then turn the white dial next to it to Top up the pressure.

@I like Skol is correct - working on a tap should NOT reduce the heating system pressure as they are separate circuits.

 

[I like Skol]

The reason a filling loop is required is to prevent the heating circuit feeding back into the freshwater supply. Radiator loops can have some highly toxic additives put into them to prevent corrosion and you MUST always remove the filler loop pipe or key to physically isolate the two systems after filling.

The separate unvented cylinder goes only to a shower cabin because the heater is a combi and it reduces the pressure loss if someone turns on a hot tap when

Still can't envisage what this is doing to overcome the problem it is described as overcoming?

 

[raleighnut]

Sounds like it needed the pump to run to equalise the pressure out, it should now fill to normal pressure if you open the feed loop valve.

 

[Bazzer]

The reason a filling loop is required is to prevent the heating circuit feeding back into the freshwater supply. Radiator loops can have some highly toxic additives put into them to prevent corrosion and you MUST always remove the filler loop pipe or key to physically isolate the two systems after filling.


Still can't envisage what this is doing to overcome the problem it is described as overcoming?

The systems are separate. Perhaps it is the way I described it, but the unvented cylinder is heated by a takeoff from the main heating system. It is a closed system and the water supply delivered by the unvented cylinder is separate from that heating it.

Sounds like it needed the pump to run to equalise the pressure out, it should now fill to normal pressure if you open the feed loop valve.

It did thank you.

 

[newts]

The filling loop is only for the Central heating circuit. The coil inside inside the hot water cylinder (that heats the water) is part of the central heating circuit controlled by zone valves (basically another radiator). The hot water inside the cylinder that you draw off via the taps does not mix with the central heating water. Therefore if you isolate the domestic hot water, the pressure on the heating circuit should not be affected. All shut off valves should have been clearly labelled by the installer, sadly rarely happens. Perhaps inadvertantly you shut off the cold water supply to the cylinder & also let the pressure out via pressure realease valve on the heating circuit.