Heating system kettleing over

[flinty]

Any help appreciated here.

The central heating system is fully pumped and has two x 2 port valves.
One for the central heating which is motorized and the one for the hot water works with a remote sensor on the tank but shuts using the same system as a TRV (not sure of the correct term for this type so if someone knows feel free to tell me).

First the pump was not running at all or just slowly and the system was kettling quite quickly so I replaced the pump, however now the system will run fine for a couple of hours and then start to kettle.
Could it be the hot water thermostat is faulty (I have tried turning it down but it made no difference).

Help please???

 

[twgas]

with next to no info who knows what the problem is but you probably need a bypass

 

[flinty]

The system was working fine then started kettling when it seemed the pump had failed.

 

[flinty]

Here are a couple of pictures of the system.

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[twgas]

think you got design probs which has crudded up your system over the years

 

[flinty]

That one has an air vent at the top and the other end goes into the tank at the top of the heating coil.

 

[twgas]

? boiler info

could be build up of crud in highlighted area, cant see for sure but looks like pos cold feed and/or open vent.

 

[JohnD]

when you say "kettling" do you mean it is making a slight noise?

Your pictures are of the cylinder not the boiler, which of them is making the noise?

 

[flinty]

What I mean is that hot water is coming out of the vent pipe at the top of the cylinder and going into the feed and expansion tank in the loft... sorry if I didn't make myself clear enough.

As the F and E tank fills it is of course spilling over hot water from the tank and the water in the cylinder is getting too hot and boiling like a kettle.

 

[JohnD]

so it is overheating.

does it continue gushing into the F&E if you turn the pump off/down?

Is the immersion heater turned off?

What temperature is the boiler set to?

How hot are the radiators?

 

[flinty]

When the system is turned off it stops gushing.


Yes the immersion heater is turned off.

The rads are a little hotter than they have been but I don't know if that is because the new pump is working better than the old one.

The boiler is set to the medium setting.

 

[JohnD]

can you see the speed control knob on the pump? What happens when you turn it to "1" or "slow"?

Have you got a thermometer to test the temperature of the water gushing into the F&E?

What happens if you leave the system running but turn the boiler thermostat right down as far as it will go?

On your picture, please identify which pipe is the cold feed from the bottom of the F&E tank, and which is the Vent pipe that curves over the top of the F&E.

 

[flinty]

The vent pipe that curves over the top of the F&E tank is not shown in the picture it is the vent from the pipe that comes out of the hot water cylinder.

At the moment the pump is set to setting '2' or med speed.

I will try it with the thermostat on the boiler turned right down as low as it will go and see what happens.

Sorry I don't have a thermometer to test the water temp but I can tell you that it is hot.

 

[JohnD]

So have you tried adjusting the pump speed yet?

OK I misunderstood. If it is not the F&E but the pipe from the top of the cylinder then I don't know. I guess your boiler must be overheating. I would guess thermostat failed

sorry

no more ideas

but please have a look in your F&E tank just to be sure water is not flowing into or out of it - this is important as it might be a completely different fault.

 

[flinty]

So have you tried adjusting the pump speed yet?

OK I misunderstood. If it is not the F&E but the pipe from the top of the cylinder then I don't know. I guess your boiler must be overheating. I would guess thermostat failed

sorry

no more ideas

but please have a look in your F&E tank just to be sure water is not flowing into or out of it - this is important as it might be a completely different fault.

Do you mean the boiler thermostat or the tank thermostat that stops the water from going through the tank heating coil?