Three way valve problem?

[shadow1964]

My in-laws system is playing up.
Recently, I have de-sludged the system using Fernox, I drained the system down, re-filled it adding the Fernox, left it for a week and then drained until water was running clear.
This seemed to work, but a few days ago, the central heating wasn't working. I have now changed the pump, and it now works, however, there are still a few problems....

The boiler won't fire up if only the CH is on, the HW has to be on too!

There is hot water going into the expansion tank.

Could this be a problem with the three way valve? I changed the motor in it today - no difference. This valve is only about 12 months old, a neighbour fitted it last year.

Alternatively, could it be a problem with the programmer?

Any advice would be most welcome, thanks.
Mark

 

[johnmcginty]

What type of system have you got? what plan? etc? hot water in the f&e tank? have you and indirect cylinder? sounds like a bust coil.

 

[shadow1964]

It's an open system.
It's an indirect cylinder.
What do you mean by bust? If you mean that water is leaking from the coil into the cylinder then the hot water (from the taps) would not be as clear as it is.

 

[sonray ltd]

then the hot water (from the taps) would not be as clear as it is.

wouldn't it whys that new one on me ?

what tank is the highest cws or f/e tank ?

burst coils don't pump over the vent they fill the tank through the feed pipe.

and as john said they feed cylinder to coil providing your tanks are round the right way.

what make/model is the valve ?

>The boiler won't fire up if only the CH is on, the HW has to be on too!

if the hw has to be on, and the rads get hot that tells me its stuck in mid position.

>There is hot water going into the expansion tank.

that tells me their is a blockage.

need more info and check one thing at a time.

 

[shadow1964]

Thanks for the reply.

The f/e tank is higher.

Can't remember the make of the valve. But my thought too was that it may be stuck, that's why I changed the motor. I'll change the valve, see what happens.

Thanks

 

[sonray ltd]

need to do some checks or your just chucking money at it for nothing.

the motor will play no part in a sticking valve.
the motor only comes into play when ch called for.

does the system pump over when on hw only ?
if you turn heating off hw on does the rads still get hot ?

 

[shadow1964]

The valve is a BossTherm BMPV222.

The rads do appear to get hot when on HW only.

Hot water enters the f/e tank even when on HW only.

When HW and CH both on the water temp in HW Cylinder is higher than the thermostat setting.

Thanks

So I guess that it is stuck in mid position then.

I'll change the valve, see what happens.

Thanks