Heating Bangs when switching off.

[Paul Cooksn]

Hi,

I have an older style open vented heating system with a Glow worm 50/60 RF flued fan boiler. I have a hot water tank on the first floor and two header tanks in the loft, one large for the hot water and a smaller one for the heating.
Last week I removed a radiator from the landing and capped off the pipes under the floor. Since doing this when the boiler switches off there is a loud bang and the whole heating system shakes. I thought it was an air lock but I have bled the system and all radiators are warm. It only does it when it's on heating, not when on hot water. Another point, when the boiler switches off water runs into the header tank for about 3 seconds.p from the expansion pipe.
I've even tried connecting the pipes I cut off together just in case I had messed up the flow and return but it's still the same. All radiators have trv's apart from a heated towel rail in the bathroom and large radiator in the hall which is by the thermostat.

Anybody have an ideas what it might be. I have also flushed the system and it is clean. It's worked fine for years until I removed the radiator.

Many thanks.

Paul.

 

[Paul Cooksn]

What speed is the pump on now?

Pump is on 2 as the system is quite large 12 rads.
Cheers.

 

[Last Plumber]

I

Pump is on 2 as the system is quite large 12 rads.
Cheers.

If it works well it's fine. You want them on the lowest setting that works and gives the right flow and return temps.

With the valve:-
screw it shut, turn on the heating and hot water so both Motorised valves are open and the pipes start to get hot. Slowly open the Auto by-pass 1/4 turn at a time, (a few seconds in between turning), until you feel hot water flow through the by-pass. Then close it back around a half turn.


That's the best explanation I can give on a Forum. I would be going to greater lengths to set things up and balance the system if I were doing this in person but it will do!

 

[Paul Cooksn]

I


If it works well it's fine. You want them on the lowest setting that works and gives the right flow and return temps.

With the valve:-
screw it shut, turn on the heating and hot water so both Motorised valves are open and the pipes start to get hot. Slowly open the Auto by-pass 1/4 turn at a time, (a few seconds in between turning), until you feel hot water flow through the by-pass. Then close it back around a half turn.


That's the best explanation I can give on a Forum. I would be going to greater lengths to set things up and balance the system if I were doing this in person but it will do!

Thanks I'll do it on Saturday and let you know how it goes.

Cheers.

 

[Last Plumber]

Thanks I'll do it on Saturday and let you know how it goes.

Cheers.

Please do come back and tell us how you went on.

 

[Paul Cooksn]

Please do come back and tell us how you went on.

Hi.

I fitted the valve where suggested and unfortunately it still bangs, perhaps even louder. I can't get water to run through the valve unless I restrict the hot water flow, even with it turned down to 0.1 bar, the lowest it will go.

Picture attached.

Cheers.

 

[Ric2013]

Does the light on the pump flash or stay solid?

 

[Paul Cooksn]

Does the light on the pump flash or stay solid?

Stays solid then switches off completely.

Cheers.

 

[Ric2013]

Okay. That's fine. If you were running it in flashing mode, then it would not be running fixed-speed, and the automatic bypass valve wouldn't be able to work as it should.

 

[Paul Cooksn]

Okay. That's fine. If you were running it in flashing mode, then it would not be running fixed-speed, and the automatic bypass valve wouldn't be able to work as it should.

I'm not sure it is. I can only get water to flow through when I restrict the flow on the hot water.

I would have thought 0.01 bar would be open all the time. Any suggestions.

Cheers.

 

[SavageW]

When you say restrict the flow on hot water,is this when the system is running eg demand from heating/hot water? The hot water coil should have a balancing valve on it that should be restricted (which from the pic you have one after the 2port) to stop the heat just whizzing around the coil and giving less to heating

 

[Paul Cooksn]

When you say restrict the flow on hot water,is this when the system is running eg demand from heating/hot water? The hot water coil should have a balancing valve on it that should be restricted (which from the pic you have one after the 2port) to stop the heat just whizzing around the coil and giving less to heating

The balancing valve is fully open. When I mentioned restricting the flow I shut it off. Are you saying this valve should be half turned off or similar. Is this likely to contribute to the banging.

Cheers.

 

[SavageW]

It should be restricted yes,but are you only getting flow through the by-pass valve when there is still demand for ch or hot water an your closing the balancing valve?

 

[Paul Cooksn]

It should be restricted yes,but are you only getting flow through the by-pass valve when there is still demand for ch or hot water an your closing the balancing valve?

If I run the water and heating separately or even both of them together I can't get any water to pass through the bypass valve. I can only get it to pass through when I close the balancing valve with the hot water on demand.

 

[Paul Cooksn]

Another point I forgot to add. If I turn the pump off at the fused spur, it doesn't bang. Don't know whether this has any bearing on the fault but thought I would mention it.

Cheers.

 

[Last Plumber]

What size of pump is it, I can't read it