Vokera mynute 28 pressure issues

[Completely Baffled]

Hi

I have a vokera mynute 28 combi boiler in the house I recently bought, The system is as follows, there a single cold water tank in the loft, a pressure vessel in the bathroom with a 3 port valve. The controller is a diadem 425.

I have been running the DHW since moving in with no issues, I put on the CH and have now noticed the pressure gauge reading drops each time I use the CH, I have topped up the system to 1 bar and in 7 hours it dropped to 0.5. I have put a bag over the outside pipe and its dry, I have depressed the valve on the tank behind the unit on top and only air comes out, i have checked for water leaks and found none.

I am a novice when it come to boilers and would appreciate any insight into my problem. I read FAQ's but they don't exactly match my problem.

 

[vulcancontinental]

Top up system. Turn off boiler. Shut off valves beneath. Do not run boiler.12 hours later look at gauge on boiler, if pressure has drpped it's the boiler, if not open valves, if pressure then drops it's system. Hope the valves don't drip.

 

[dilalio]

I have depressed the valve on the tank behind the unit on top and only air comes out,

Do you mean the expansion vessel? Is this valve you depressed like a car tyre inflation valve (Schroeder valve)?
If so then you have depleted the air side of the vessel and this should have an air charge as indicated on the side!

 

[ianmcd]

Do as Vulcan says and if it losses pressure with the valves closed you will probably need a new heat exchanger, and as he correctly says you might need new isolation valves too after you open them again

 

[Completely Baffled]

Top up system. Turn off boiler. Shut off valves beneath. Do not run boiler.12 hours later look at gauge on boiler, if pressure has drpped it's the boiler, if not open valves, if pressure then drops it's system. Hope the valves don't drip.

I depressed the value momentarily, just a quick release.

 

[Completely Baffled]

Top up system. Turn off boiler. Shut off valves beneath. Do not run boiler.12 hours later look at gauge on boiler, if pressure has drpped it's the boiler, if not open valves, if pressure then drops it's system. Hope the valves don't drip.

Thanks I will give this a try at the weekend and report back, is there a special key or tool to shut the valves with?

 

[ianmcd]

yes its called a spanner

 

[Completely Baffled]

thanks

 

[Completely Baffled]

I have isolated the boiler for 12 hours as you have suggested and pressurized before shutting the valves. There is no drop in pressure on the boiler.

Assuming there is a leak in the heating coil, is this something that needs to repaired or can it be topped up daily?

Are there any other checks to narrow down the fault to the pressure vessel upstairs?

Thanks

 

[dilalio]

Well after you described letting air out of the Schrader valves the ev, I be checking that you haven't depleted the charge on the air side!

 

[Completely Baffled]

Top up system. Turn off boiler. Shut off valves beneath. Do not run boiler.12 hours later look at gauge on boiler, if pressure has drpped it's the boiler, if not open valves, if pressure then drops it's system. Hope the valves don't drip.

I have done as you said and there no drop on the boiler, what items can i check when you refer to the system?

 

[Completely Baffled]

Well after you described letting air out of the Schrader valves the ev, I be checking that you haven't depleted the charge on the air side!

I gave it just a short press and still pressure on the air side.

 

[Completely Baffled]

Well after you described letting air out of the Schrader valves the ev, I be checking that you haven't depleted the charge on the air side!

what should the pressure be on the Schrader valve?

 

[dilalio]

I gave it just a short press and still pressure on the air side.

But how much pressure? You need a foot pump with a gauge on it and you need to ensure it is charged to the correct pressure, as indicated on the side of the vessel - and this needs to be done without any pressure being applied from the water side of the vessel which means letting water out of the system, charging the air side to correct level, then filling the system back up to appropriate pressure!

 

[dilalio]

what should the pressure be on the Schrader valve?

See label on side of ev for specs.