Central Heating "Kettling"

[Rolyan]

We have a Myson Economist gas fired boiler running a central heating system, with 6 radiators. There is a primatic cylinder in the system. It is all about 15-20 years old, but it's been serviced regularly. It worked well until about 18 months ago, when we had a radiator moved (only a few feet) months ago, and thermostatic valves fitted to all the radiators.

After a few weeks, we noticed 'kettling'. When the engineers who had done the radiatorsl ooked at it, they changed various things, over several visits, and the last change was the thermostat in the boiler. This seemed to work (although I don't know why this should be).

It hasn't kettled for about 12 months, but we turned the valve down on a downstairs radiator the other day, and its been doing it since then. The system seems to run fine on start up. After a while, the boiler starts to 'kettle', and the thermostat kicks in and switches the boiler off. This gets worse and worse, until we have to switch everything off. It does this almost every day.

I've tried bleeding the radiators (wishful thinking!) but they were all fine. However, two of them didn't bleed very well. Hardly any water came out even when the small plug was completely removed.

I wondered if there was air in the system, but I don't know where this would have come from, and if it would cause the problem. Any help on this would be most appreciated, as we need to call in the experts again, and I would like to have some idea before we start paying out to change everything.

 

[Johndug]

Is the pump working? Providing at least one rad valve is open, water should squirt out when the bleed valve is opened.

 

[Bahco]

[quote=" thermostatic valves fitted to all the radiators.

[/quote]
Is there a bypass fitted? Could be the one rad (acting as a bypass) that you have turned off. Try opening both valves on this rad which should not have a trv if bypass is not fitted

 

[kevplumb]

ye gods you actually read the book

 

[Rolyan]

When we tried bleeding the rads, we did it with the system off, as we thought this was what you're supposed to do. So the pump wasn't on, but only 2 rads failed to bleed properly, out of 6. All the valves were open. It kettles even with all the valves open, so I dont think its the bypass problem (although I'm not even sure what that is). Should you bleed with the system running, or off?

However...the heating has just done the kettling again, and when I checked the pump (located in the airing cupboard next to the tank), it doesn't seem to be running. It's a Myson Compact CP53 code 1194. It's probably quite old. There was a slight vibration, but hardly anything. Am I correct in thinking that if the pump didn't work, the water wouldn't move around the system, so it wouldn't leave the boiler, so this could cause it to kettle. Or am I totally confused by my lack of knowledge? If I know it could be the pump, I can talk to the Plumber with some confidence.

Also (one last question, please bear with me) is the pump meant to run the whole time the heating is on, or only when the boiler is fired up and running.

Many thanks for the comments so far, believe me they help.

 

[Rolyan]

[quote=" thermostatic valves fitted to all the radiators.

Is there a bypass fitted? Could be the one rad (acting as a bypass) that you have turned off. Try opening both valves on this rad which should not have a trv if bypass is not fitted [/quote]

see below for the details, thanks for your comments.

 

[kevplumb]

undo the screw in the middle of the pump sharp know if its running or not

 

[Rolyan]

undo the screw in the middle of the pump sharp know if its running or not

I've just tried to do this, but it seems extremely tight. You can't move it by hand, and would need pliers (after pulling off the hexagonal cap or cover). Is this correct, or should it be quite loose.

If I did manage to undo the screw, what would I look for. How would I know if it is running or not. Very basic I know, but thats the extent of my knowledge.

Thanks for your help.

 

[kevplumb]

if you undo the screw you will feel the shaft turning the screw dosent come right out