Central Heating Air Vents

[justintime01]

I live in a bungalow with open vented vented heating. One of the pairs of 15mm downpipes, of which there are five pairs, feeds radiators in two adjoining bathrooms. Where these two pipes turn down from the loft they each have a 450mm tall x 15mm pipe upstand topped by a thumbscrew air vent. I recently had a new heat exchanger fitted to the gas boiler by a local gasfitter/plumber after which the bathroom rads did not heat up. I went into the loft where I knew there were these air vents and I vented one of the pipes after which the bathroom rads heated up for a day or so. The rads then went cold again so I repeated the process on the same air vent. This on/off process continued for a week or so by which time I was getting browned off. I then tried venting the other pipe after which the two rads worked ok for about two weeks but then went cold. I vented one of the pipes again which brought the rads back on but now that vent is leaking. I have had to wrap some rag around the leaking vent and drape it into a bucket to collect the drips while I await the plumber to call me back. The rads are now working OK. but I am having to drain the collected water daily.
I am a bit fed up with these thumbscrew vents as I find they have to be tightened with pliers. Finger tightening does not seem to work. My assumption is that vents for these two particular pipes were found to be necessary when the central heating was installed or modified some years previously, and this brings me on to two questions which I would be grateful if someone could answer.
Firstly, would one expect the pipes to the two radiator feed pipes to be blocked by air so frequently following the boiler work. Secondly, are there better and more reliable air vents that could be installed in place of the thumbscrew vents.

 

[HERTS P&D]

Your system could be pumping over or/and a blocakge.

What speed is your central heating pump on? Try and turn it down a speed.

Andy

 

[justintime01]

Alas it is already on min power rating. It used to be on max power from the time I moved here in 2007, but a couple of years ago it started pumping over so I was advised to turn the pump power down. To the best of my knowledge it is not pumping over now but I will check again.

 

[Johntheo5]

What vent/cold feed arrangement do you have?, is the pump on the boiler flow and from the boiler do you have, vent, cold feed (no more than 150mm between them) and then the pump which should be pumping into either a mid position valve (y plan) or a number of two port valves, (S plan).

 

[justintime01]

Johntheo,
I think the vent/cold feed arrangement is pretty much as one would expect. I cannot see the spacing between the vent and cold feed connections as the connections are close to the roofing eaves and covered with loft insulation. As I mentioned, we are in a bungalow so the loft is immediatly above the ceiling of the ground floor The boiler is wall mounted in the kitchen close to the ceiling and an outside wall. The pump is at floor level in the loft about a metre from where the pipework from the boiler enters the loft. There is a bottle air vent close to and on the "pull" side of the pump. When he changed the boiler heat exchanger the gas fitter removed the valve from the bottle air vent and cleaned it out I think. About a metre from the pump is a Y plan valve. Hope that answers your questions.

 

[Johntheo5]

Probably a partial blockage around where the cold feed is teed into the system but would require cutting out to check it, pump on min speed should not cause any pump over or air ingress, what make/model is it?.

 

[justintime01]

Sorry, I cannot tell you the make/model of the pump. The pump details plate faces away from the loft walkway and my balance is now insufficient to risk walking on joists to read the plate. I seem to recall, from my more agile days, that the working part of the pump was replaced (not the water inflow/outflow part) by the firm that replaced the old boiler in 2011 and that the pump part was a well known make e.g. Grundfos or Wilo.