Central heating issue

[mickstreet]

Hi,

I'm after a bit of advice please. I have a basic hot water / central heating system that is pumped and uses a hot water cylinder. I have a 3 way diverter valve and the usual controller and stats.

The problem I had was with the central heating. If the programmer was switch to on (auto or manual) and the stat was set to high (ie in a situation when the heating should come on) then sometimes the boiler and pump just wouldn't switch on. This was intermittent and worked probably 50% of the time. The hot water side worked fine. The c/h stat and timer are old and my dad had already repaired the board in the programmer a number of years ago so assumed that the problem lay with one of those. Yesterday I replaced the stat and programmer and all seemed fine.....

Until today when I again have the same problem. C/h not working whereby the hot water does.

I'm unsure of how the boiler gets told to switch on. Is this done via the diverter valve? When the c/h doesn't work if I mess around with the hot water to force the valve to move then eventually the c/h will fire into life. I'm "thinking" that the signal to the boiler is sent from the valve and as such this is faulty however it does seem to move to any of the 3 positions fine. The valve is a Drayton BGMVSP-23 and if I remember rightly I changed this around 5 years ago. The only other thing it could be (than the boiler!!) is the pump and I can't see this being used to activate the boiler??

Anyone got any ideas before I spend another 60 quid to try and sort it!

Many thanks

Mick.

 

[Agile]

The motor valve acts as a relay to bring on the boiler.

It might be a faulty microswitch or the mechanism is worn and not firmly pushing the switch.

Not the easiest model to fault find on so most just replace them!

Tony

 

[D_Hailsham]

When the problem occurs, is the HW on or off at the timer?
If on, turn it off. Does the problem go away?

If it doesn't there is a wire missing from timer HW OFF terminal to valve grey wire.

If the problem only occurs when HW is set to ON, there is a wire missing from the HW stat to the valve grey wire.

The grey wire should be connected to two other wires: one from HW OFF; the other form cylinder stat SAT terminal.

 

[mickstreet]

Appreciate your quick responses.

Agile, thanks for confirming the signal to the boiler is sent via the actuator, I'm fairly certain now that is where the fault lies.

Hailsham, the fault is intermittent but has occurred both when h/w is on or off at timer. It either sorts itself out after time and then works again for a few cycles or if I make the actuator "work" by switching the h/w on and off a few times to exercise the valve then this sometimes fires the c/h into life.

It's just a pity I've had to spend £100 ish to replace timer and stat and be no further forward! IS Screwfix the best bet for a new actuator? Could do with getting it sorted over the weekend.

Thanks again,

Mick.

 

[D_Hailsham]

It either sorts itself out after time and then works again for a few cycles or if I make the actuator "work" by switching the h/w on and off a few times to exercise the valve then this sometimes fires the c/h into life.

The valve could be sticking.

Remove the actuator and check how easy it is to turn the valve spindle. It may only move 10-20 degrees between stops - depends on make of valve. If it's stiff, apply a little silicon lubricant to the spindle. WD40 is not recommended as it will rot the O-ring seals.

Actuators are not interchangeable; you must buy the correct actuator for your make and model of valve. Screwfix may have them in stock, otherwise try a plumbers merchant.

 

[Agile]

There is always a possibility that the shaft is tight.

Later heads are removeable but earlier ones were not.

If you can take off the head then you can feel the shaft, they should turn with difficulty by men's fingers and easily with a small spanner.

WD 40 will slightly ease a stiff spindle but they have two seals and it only gets to the outer seal so is not a 100% cure.

Tony

 

[mickstreet]

Guys, thanks for the advice. Got a new actuator from Amazon, wired it in and hey presto all is well. Pity I had to fit a stat and programmer just to find out they weren't at fault but there we go.

Thanks for your advice!