Grant Vortex Condensing combi 26 - pressure gauge help

[kaleyboy]

Hi, hope this is posted in correct place, my apologies if it's not.
I have two boilers plumbed into my central heating system. One is an LPG boiler fitted inside, other is gas-fired grant vortex condensing combi 26 boiler which I have in a brick shed outside. Both can be isolated by valves to switch between boilers. Last year I had some work done by a plumber on my grant vortex. I was at work and my wife was at home. When I got in, I noticed he'd disconnected pressure gauge on my grant vortex, and left a note saying I should use gauge on LPG boiler to re-pressure the system. No idea why this was. I'm now unable to reach him by phone. Problem is, I use my oil boiler as main boiler, so when needing to top up pressure, have to switch all valves to use my LPG to pressure system. I would like to re-connect my pressure gauge on my oil boiler grant vortex, but have no idea where it connects to. There is just black wire from gauge with brass nut at the end with a copper sensor, but where on the grant vortex does it connect? I know I need to drain the boiler to do it, but really need to know where the sensor and brass nut connect. Been driving me mad this one, any help very much appreciated. Thanks.

 

[Richardthe3rd]

There is every chance the gauge connection is shown on the boiler installation details. Which will be freely available on-line.

 

[kaleyboy]

No, checked that already. No diagrams or instructions at all online or in the boiler installation manual, which I have.

 

[Boilerman2]

I suspect he may have replaced the boiler safety valve with the wrong type, the correct valve has a connection for the system pressure gauge I cannot think of a more logical reason for disconnecting it other than a new safety valve had no port on it to connect to - Grant supply two different safety valves a 2.5 bar internal boiler model (with gauge port) and a 2.5bar external boiler model with no port - I think you should be able to see where I am coming from

 

[kaleyboy]

I suspect he may have replaced the boiler safety valve with the wrong type, the correct valve has a connection for the system pressure gauge I cannot think of a more logical reason for disconnecting it other than a new safety valve had no port on it to connect to - Grant supply two different safety valves a 2.5 bar internal boiler model (with gauge port) and a 2.5bar external boiler model with no port - I think you should be able to see where I am coming from

Right! That's it, 'cos the PRV fitted has no port to connect anything to. So I guess there's nothing I can do except replace the PRV?

Now I have a new problem: no hot water. Central heating works fine and boiler fires as normal, but won't fire up when hot water tap is on. I'm thinking it's the flow switch, any way to test and isolate the problem?