Whooshing in airing cupboard/boiler pumping over

[alastairpearce]

Hello,

Never posted on this forum before, so please bear with me.

A problem occured with our central heating/hot water about a months ago. There was a loud noise coming from our airing cupboard, which sounded like whooshing coming up from the boiler downstairs. This gradually increased in volume until the pipes were shaking in the airing cupboard and there was a loud release of hot water/steam into the expansion tank in the attic.

My system details are:
Ideal Classic LX RS260 Boiler
Grundfos Selectric 15-60 pump
Honeywell motorised 2 port valve
Myson aerject de-aerator
Danfoss ravi thermostatic cylinder valve

Initially, I thought a blockage in the system might have caused this pumping over into the attic. I have had the system powerflushed, but this proved unsuccesful in solving the problem.

I also installed a brand new pump, but this was also unsuccesful in curing the problem.

Subsequent to this, I identified some pipework in the airing cupboard which had blockages in, so I cut out the pipework and did a like for like replacement. I no longer think a blockage in the airing cupboard pipework is the problem because I have checked all the pipes with magnets and there is no attraction, and water seems to be flowing freely through the system.

I have also removed and checked the Danfoss thermostatic cylinder valve, and tested the thermostatic sensor to ensure it is functional, it is working fine.

The boiler stat is set to 3, and the boiler is still producing boiling water and pumping over. I previously thought the boiler thermostat was functioning fine, because the boiler stat turned off the boiler when the stat was turned down, and fired the boiler when turned up.

But could the boiler thermostat still be faulty even though it turns the boiler on/off?

When the boiler stat is turned down to 2, the problem still occurs althought it takes longer to occur. With the stat turned to 3 last night it was running fine for 1.5 hours before the pumping over occurred again.

This problem only occurs when I require hot water only (i.e. the motorised valve is not providing water to the radiator circuit).

I thought I had diagnosed and cured the problem, but I am all out of ideas now and cannot think what the problem could be.

If anyone can help I would be most grateful.

Thanks

 

[mysteryman]

Does the Danfoss RAVI valve switch the boiler off or just close off the circulation, leaving the boiler to fire? [I haven't seen one for years.]

If so, it is a poor system layout, and should be changed to one with two 2 port valves and an electric cylinder thermostat.

 

[simond]

In the first instance, I would remove the Danfoss RAVI and insert a piece of pipe.

 

[alastairpearce]

Does the Danfoss RAVI valve switch the boiler off or just close off the circulation, leaving the boiler to fire? [I haven't seen one for years.]

If so, it is a poor system layout, and should be changed to one with two 2 port valves and an electric cylinder thermostat.

Thanks for your reply.

The Danfoss Ravi is a 3 port thermostatic valve, so when it closes the circulation goes through the bypass loop, rather than through the hot water circuit in the cylinder. Thus, the system relies on the boiler thermostat to shut itself off.

I realise this is an inefficient layout, but the boiler has been installed for over 10 years and I'm curious why the fault is only occurring now?

 

[simond]

I looked up the RAVI and it came up as a two port. If your is a 3 port then I concur it is unlikely to be the problem.

Next step, change boiler stat.

 

[namsag]

Your boiler stat has gone and needs replacing. Even though its at number 3 its allowing the boiler to heat to equivalent of 7 or 8.
When you have heating on the rads are dissipating the heat more than just HW on but would eventually start banging to if left on long enough.
Some classics come as a 2 part stat ,the sensor and the bit the knob is connected to has a little resistor on it .Change them both if this type

 

[alastairpearce]

Your boiler stat has gone and needs replacing. Even though its at number 3 its allowing the boiler to heat to equivalent of 7 or 8.
When you have heating on the rads are dissipating the heat more than just HW on but would eventually start banging to if left on long enough.
Some classics come as a 2 part stat ,the sensor and the bit the knob is connected to has a little resistor on it .Change them both if this type

I agree as far as I can tell I have narrowed the problem down to the boiler.

If it's not the boiler stat then I really don't know what it could possibly be. Therefore I think I'll try changing the stat before spending big money on overhauling the system.

So what do I need to do to change the boiler stat. Is this a job for a Gas Safe engineer, or can I do it myself? Do I need to order the parts myself, or would a Gas engineer have the parts?

I appreciate your help, thanks.

 

[bengasman]

Thinking/guessing the flow in the system is sufficient is no good. You need to test it/prove it.

 

[alastairpearce]

Thinking/guessing the flow in the system is sufficient is no good. You need to test it/prove it.

I've had the system power flushed; I've identified blockages in the airing cupboard and removed the blockages. I have subsequently tested all the peipes in the airing cupboard with a magnet and can't identify any further blockages in any of the pipework that can be accessed.

Also, when removing the blocked sections of pipework I connected the bathroom tap upto the indirect coil going through the hot water cylinder and water flowed through this fine and only a tiny amount of sludge came out.

I've had a new Grundfos pump installed, so it can't be an issue with the pump.

And the hot water works fine for a period of about 2 hours before the pumping over issue occurs, which suggests it is almost working fine but not quite.

Lastly up until 2 months ago the system has worked fine for 2 years since we moved in the house.

Thefore, I honestly don't think it is a problem with circulation as I believe I have done all that I can to ensure that the circulation is fine.