TRV-passing air?

[jessejazza#]

I would be grateful if someone could explain how on earth air can enter the supply pipe on the radiator. The rad in my hall has a 'cheap TRV' i.e NOT Honeywell or Drayton type worth £25-£30. I didn't fit it - it was in the house when i moved in and each rad in the house has the same. TRV is on supply and lockshield on 1/4 turn open return pipe.

When i started the central heating and bled all rads the one in the hall still had air in it somehow. So there was gurgling and seemed no way of stopping it. I took the head off checked the pin was ok (i can only assume that air can pass the pin). I changed the head for another and the result was worse!

I'd just be interested to know how this can happen. Everyone fits TRVs and to be honest i don't like them. When the boiler was serviced a month ago i had the valves replaced for mechanical and all is fine.

 

[fixitflav]

When i started the central heating and bled all rads the one in the hall still had air in it somehow. So there was gurgling and seemed no way of stopping it. I took the head off checked the pin was ok (i can only assume that air can pass the pin). I changed the head for another and the result was worse!

There should not be anywhere in the system below atmospheric pressure, so in theory that shouldn't happen. The pressure datum, either the connection from the F/E tank or the expansion vessel, should be as close as possible to the pump suction, to ensure the pressure everywhere else is higher. If that's not the case it might explain things.

 

[jessejazza#]

The boiler is an outside combi with expansion vessel. The house is a bungalow. "to ensure the pressure everywhere else is higher." - see the point you are making and thanks. Other rads are ok and the Hall one is fine now with manual valves. So somehow the problem had to be that hall radiator. A possibility could have been a slight leak but I checked for that.

I've got little faith in TRVs. I had them put in for my mother and a small utility room which got warm quickly never seemed to get turned off with the TRV. I thought the whole point of the TRV was that when the room got hot it turned the radiator down/off. I prefer a manual valve and use a fridge thermometer (as they are accurate) to adjust the supply/feed valve to 20 deg which is the same as the room thermostat in the hall. I do that in each room and all rooms seem to keep the same temp.

 

[fixitflav]

The boiler is an outside combi with expansion vessel. The house is a bungalow. "to ensure the pressure everywhere else is higher." - see the point you are making and thanks. Other rads are ok and the Hall one is fine now with manual valves. So somehow the problem had to be that hall radiator. A possibility could have been a slight leak but I checked for that.

I've got little faith in TRVs. I had them put in for my mother and a small utility room which got warm quickly never seemed to get turned off with the TRV. I thought the whole point of the TRV was that when the room got hot it turned the radiator down/off. I prefer a manual valve and use a fridge thermometer (as they are accurate) to adjust the supply/feed valve to 20 deg which is the same as the room thermostat in the hall. I do that in each room and all rooms seem to keep the same temp.

Good it's sorted. I've got Honeywell TRVs which work OK. Older than 24 years as they were here when I moved in in 1998. Only problem I had, a few years ago, was one started to chatter loudly. I tried turning down the internal throttling ring but no help. So I took the head off and throttled on the manual valve, and it worked about as well as the TRV. I thought about swapping the TRV head with another to see if the problem was the valve or the rad but never got round to it. Then a couple of years ago I refitted the head and opened the manual valve, and the problem had disappeared.