Central heating failure


Postby markp3532 » Fri Nov 30, 2007 4:12 pm

Hi folks,
My C/H failed big style, after a plumber fitted a new shower pump in the loft and a new immersion tank, the pump appeared to be running, but non of the rads were heating up. The boiler kept cutting out as you could hear loads of air in the system.

The update is as follows - I have fitted a brand new 3 speed pump in the airing cupboard, drained down the system several times and run fresh water from the header tank in the loft, untill the water ran clear. I also tooke off a rad which didn't appear to be filling up properly, cleaned/replaced it.
I filled up the system and hey presto - nothing !! still no heating. The pipe just after the mid position valve is piping hot, but six inches below that it is cold - which makes me think that the water is not being circulated, the boiler (Gloworm 50FF) still cuts out as the water inside it is hot, so it thinks that it has done its job and stops as (i think) it should.
Have i missed something obvious or am i just cursed ?
Has anyone got any ideas that wont cost several hundred pounds .
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Postby marrtin » Fri Nov 30, 2007 11:18 pm

It could be an airlock, but it is a little unusual to see nothing at all getting hot. Have you made sure both valves on either side of the pump are open?

Is there a bypass open that is allowing the water to short circuit the system?

Is the hot water being pumped around the cylinder coils? Is the restrictor valve open too far? Try turning the hot water off at the programmer. Does this make the rads work?

Open the mid pos valve by pushing the lever over to the right and hooking it into the slot. Does that work then?
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Postby markp3532 » Sun Dec 02, 2007 10:30 am

Marrtin, thanks for that, both valves are fully open, the pump itself is hot and is pumping, the mid pos valve appears to work correctly.
Dont know about the restrictor valve !! Where would i find it and how do you guage if it is open to the correct position.
Thanks again
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Postby marrtin » Sun Dec 02, 2007 10:00 pm

If you trace one of the pipes from the 3 port valve, it feeds into the cylinder about half way up (which is the heater coil) then in the same position, but about a foot lower it comes back out, and connects back to the return pipe of the heating system. Somewhere along this length should be a gate valve that restricts how much of the water circulates the DHW side of the system.

This valve should be only slightly open. Close it fully, and crack it open just enough to hear or feel the water begin to flow (1/2 - 1 1/2 turns maybe). If it is open too far, the radiators very possibly will be robbed of hot water.

Before you alter this, if the cylinder is not getting warm you have a problem elsewhere, and this will not solve your problem.
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