Overflow of Hot Water

[Rumbler]

Hi guys

I'm new to the site & as you will no doubt find out, new to certain areas of DIY!!

I've recently bought a house & now have a problem with the hot water. I have an Ideal boiler & an open vented system (large & small tank for hot water in the loft?).

The hot water is timed to come on at 6am, and then switch off at 7am. At about 6:50 we sometimes get hot water pouring out the overflow pipe at high level, at the rear of the property. This only lasts for a minute or so & only right at the end of the heating cycle.

So does anyone have any clues? I've trawled other sites but it's driving me insane! I'm slowly thinking it's a faulty thermostat on the cylinder, forcing hot water back up the system.

Hot water is now off & I've turned the thermostat on the cylinder down to 50degC. Not touched the boiler thermostat yet though.

Any help would be of great use! Thanks.

 

[duffin]

as the water in the cylinder expands, it is returned to the large storage tank in the loft. sounds like the ball valve has been set too high so when water returns it overfills so goes out the overflow. does the ball valve have a brass arm? if so, try bending it downwards. this will reduce the height in the storage tank so any excess stays put!

 

[Rumbler]

Thanks duffin

The small tank appears to be the one with the ball valve. This appears to be set well below the overflow pipe.

 

[Hugh Jaleak]

Really need to know which cistern is overflowing, but my money is on F&E (small) cistern. Hot water cylinder isnt going to cause enough expansion for water to gush out the overflow, even if the level was too high in the cold storage cistern initially, it would just drip.

As you've said 'right at the end of the heating cycle', i'd be confident its the system 'overpumping'. The pump starts whacking the water into the F&E cistern rather than round the system. Pump puts water in faster than the cold feed can put it back, so it overflows. Once system has shut down the level in the F&E will slowly drop, fresh water will be added as necessary from ballvalve. Adjusting stats wont achieve much, problem is more complicated than that! Really needs looking at and sorting out, pumping over is not good for the health of the system.....

 

[yerino]

Not really sure what Duffin is talking about.

The problem is with your feed and expansion tank (central heating) and you have a "pumping over" problem.

The result of this is probably a blockage forming within your pipework (normally near where the cold supply from the tank meets with the CH pipework.)

You can sometimes get around this by -

Turning your pump speed down.
Raising the vent pipe going over the F+E tank.

Ultimately you need to sort out the forming blockage though.

Pumping over is not good for your system and will soon start to corrode your radiators, etc.

 

[Rumbler]

OK, thanks guys.

How come the "over pumping" takes 50mins to cause an issue?

Sounds like I may need to call in British Gas!

 

[TicklyT]

How come the "over pumping" takes 50mins to cause an issue?

50 minutes may be the time it takes to heat your hot cylinder until the cylinder 'stat switches, moving a motorised valve, then the system could start pumping over if there's a pipework configuration or a control issue.

A control wiring or switching error may continue to send a 'call for heat' signal to the boiler even if the both the cylinder and heating controls are 'satisfied', so the system has nowhere left to send the boiler's output.

Or it may just be a badly sludged up system.

Once pumping over starts, it usually gets worse, as it introduces fresh oxygenated water into the system, corroding radiators and forming more sludge.

 

[Rumbler]

The Honeywell controller does seem a little dodgy upon further inspection. Kind of flickers between things/settings.

Sounds like I need to ring someone in the morning to take a look, diagnose/fix the issue & flush out the system.