Alpha 280E heating / pressure

[herbie2]

I have an Alpha 280E, the heating will come on when put on constant but after a while (15 mins'ish) at temp the pressure meter is very high and after a while the top orange light comes on and the system dies. Can restart straight away by switching from ON to OFF manually. The hotter the thermostat setting the higher the heating water pressure is. "Very hot" sends the meter beyond setting 4!!! Probably dangerous. There seems to be allot of relay switching and false starts before actually firing up the gas. Radiators get hot and hot water temp fine. Anyone got any advice as to what is wrong?

 

[herbie2]

Correction to my posting. I meant from ON to OFF then ON again manually. Can get it to work with the timer set to 1 segment ON then 1 segment OFF then ON ....... It's 4am and cold. HELP

 

[Slugbabydotcom]

"Very hot" sends the meter beyond setting 4!!! Probably dangerous.

Yes it is dangerous STOP USING IT.

I have seen one case where the pressure relief pipe was dripping and some bright spark decided to put a stop end on the pipe to stop the leak. A very dangerous practice indeed. I mentioned it because that could be the case here. If not then the pressure relief valve is stuck or the pipe is otherwise blocked. a dangerous situation in any case.
A faulty pressure vessel is also indicated and perhaps a fault with a thermostat or thermistor.

 

[herbie2]

Hi, thanks for the advice and rapid reply.

If I have the thermostat set to about 1/4 (3 o'clock) the pressure meter shows about 2.2 bar. Orange marker is from 2.5 upwards. Had a look at the pipe from the outside, with the aid of a torch it's still dark here, no drips or steam.

Sounds like a job for the professionals, or is there something I can check with the aid of a multimeter etc?

Cheers

Herb

 

[ChrisR]

The pressure relief valve should be letting water out at 3 bar. If it isn't doing that, it needs sorting out, before we proceed to get the boiler going.
First thing to do would be change the valve.

 

[herbie2]

Thanks for taking the trouble to reply.
I assume these are straightforward to get hold of and fit?
Just turn off, make sure temperature is cold and replace?
No special tools, etc?

 

[Paul Barker]

It's front right red knob, isolate flow and return, drain boiler, undo compression union with discharge pipe, undo grub screw with manifold and pull it off. Fit new one, open flow and return, repressurise through filling loop, purge air (ensure auto air vent is open, cycle boiler bwetween heating and hot water, as soon as it lights, turn it off, when pump stops giving air a chance to escape alternate to hot water and vice versa).

 

[herbie2]

That sounds fine, but my one doesn't appear to have a grub screw. There is a screw above the pressure valve which looks like it is something to do with the device above the pressure relief valve. Is this what needs to be removed?
How do I check that the auto air vent is open and what / where is it in the system?
I will try and get a new pressure relief valve today.
What looks like a thermostat fitted to the left most brass unit has had a leak at some time (don't know if this needs replacing). How do I check it?
Sorry for the long list of questions.

 

[ChrisR]

I don't see any grub screws Paul.
AAV cap is arrowed

Thermostat sensors often weep - nip it up a bit.

 

[Paul Barker]

OK it's a no. 0 philips screw that reatains the male push in o ring sealed part.

 

[herbie2]

Thanks guys

I shall let you know how I get on.
If I haven't blown myself up in the process.
Just one question how do I check that the auto air vent is open?

 

[kevplumb]

Just one question how do I check that the auto air vent is open?

the black cap should be loose