Mynute 20e losing pressure

Hi,

Original system was a pressurised feeding the radiators and hot water tank. Then...

Plumber fitted thermal store, wood burner on top of existing gas system. Woodburner, open system attached to radiators and volume of thermal store. Boiler pressurised, flow and return into a coil in the thermal store + there was a rad 10 ft from the boiler that was across the send and return. All was working (although I do have a bit of an issue with balance of heat to the room vs water for the fire).

A to-do for the plumber was to take the radiator off the send a return (otherwise it would only be used when the boiler was firing), he came out and disconnected the rad from the send and return and put it onto the rad circuit.

From then, you set the pressure, the boiler fires, the pressure goes up to 3 bar, then over the next hour or so pressure -> 0. Next time the timer gets boiler to fire, insufficient pressure. Plumber says he doesn't do this boiler and doesn't know what is wrong - he has spent an hour or so on it.

So I have:
- emptied water and checked the pressure vessel.
- There is a left on Honeywell on the send or return next to the hot water tank. I was concerned that this may be in the off position - so opened the valve that sits between the send and return on a conventional system, but it did the same.

1) So just trying to remove variables and one is the flow / return valves at the bottom of the boiler - I've searched and can't see how these work, they have a screw that is tight. How can you tell if they are open / closed? I don't want to fiddle unless I know how they work.

2) Can someone walk me through the fault find.
Cheers,
Jason

Just to add:
I have collected water from the PRV, but don't think this is the problem it seems to me to be that the pressure increases to 3 bar which invokes the prv.

What was the pressure in the expansion vessel ?

Hi, I set it to the manual figure for the 20e (.8 bar).

The flow / return valve under the unit, do you use a screw driver to loosen the the screws and then turn the valve or is the screw the valve control?

I was thinking of putting in a link where the rad was taken out, then if if the pressure doesn't spike, then it is a blockage in the send / receive.

Also, the pump doesn't have a I II III does it? It is now only having to drive the water to/from the tank and not all the way round a system, so thought it may be constriction in the coil in the tank?

Thanks for picking up the thread, look forward to working through it.
Regards,
Jason.

Dont worry about the flow and return valves at the moment, if one of them was closed the boiler would overheat, check the pipe that connects between the bottom of the expansion vessel and the pump for a blockage.

OK, I think you may be onto something. This AM, when pressure guage said 0 bar, I checked the expansion pressure, it said 1 bar (Obviously I had set it a little higher than the 0.8 it was supposed to), then filled the circuit to 2 and then 2.9 bar and checked the expansion again and it still said 1 bar.

My car tyre guage works correctly as I have used it in the past couple of days on car tyres. So to a potential blockage.

You would expect the pressure in the bladder to be equal (or more) than the pressure of the water?

You have the bladder container at the back of the boiler with a connector onto a flexible pipe (metal webbing coated), that goes into the top / back of the pump / self bleed housing. Where is most likely to be blocked and in which order would you tackle it?

undo the top and ensure ware is coming out (item 2 on the diagram on page 32 of installation manual)?
The other end seems to have a lock pin, which I assume I pull out to release the bottom of the pipe?
Adjacent to the pipe (where it enters the pump) is a finger tight bleed valve, how should this be set?
TIA - I actually feel like I am getting somewhere after 3 months (I've been waiting for another plumber to call me back [was supposed to be here monday last week]
TIA.

You will have to drain the boiler down (good luck if you decide to use the isolation valves under the boiler) isolate the electricity and remove the pipe from the expansion vessel, they normally block near the pump then use a coat hanger or similair to clear any dirt out, (easy to tell if its cleared just blow down the pipe) the air valve cover should be left loose.

OK, a little less haste and I think your wise words would have been useful! Sort of at wits end, so just went ahead.
So:

• 
  Didn't isolate leccy
  Did drain down system (still need to put a drain point on after 1st plumber removed the one by removing the rad from the circuit)
  Didn't relieve pressure in expansion vessel

Can you guess what happens next.....
Undid nut closest to expansion vessel, got very wet as did the internals of the boiler. Very silly of me not to turn leccy off, but no harm done.

Realised should have taken end off closest to the pump as you could probably let that drain immediately outside the unit. Took pipe off, it was blocked with red sludge. Pressured it through with tap water. Put it back together, pressured it up (it took a lot longer as you would expect as it was now pressurising the vessel). Fired it up and the little red light came on. Pretty sure water in somewhere, so turned leccy off, opened protective on PCB case, hair dryer on, a lot of care taken (horse, door bolt), an hour later, all firing, working and no pressure lost after another hours operation. I DON'T RECOMMEND YOU FIX THINGS THIS WAY, BUT I'M AN ADULT AND MAKE MY CHOICES.

So, picasso, I owe you a beer. Amazed my initial plumbr was so stumped, if I would have known it would have cut out from overheat before over pressure if there was a blockage in the flow / return, it would have twigged about the expansion vessel not doing what is logical (i.e. getting to same pressure as water) and the pipe would have been first port of call as the pump mechanism is more involved. Looks like you have helped a lot of people guaging the thanks yo have. Know anything about blown air heating?

Glad you got it sorted without killing yourself or the boiler and I know bugger all about blown air heating