Central heating problem

[ASDAW]

Hi,
I wonder if anybody can help me out there ?

I have an Ideal Minimiser FF40 fanned flue boiler.
I can't get the boiler to light if I just have central heating selected even with the room stat up at full.

If I put on the hot water then the boiler will fire up but only the upstairs rads get hot, downstairs they remain cold.

I have had this problem before but it went away after switching on and off HW/CH several times.

Are these 2 symptoms caused by the same problem or are they unrelated? I seem to recall another post reply stating the pump could be at fault for the rads problem.

Any suggestions would be gratefully received.

 

[mogget]

Are these 2 symptoms caused by the same problem or are they unrelated? I seem to recall another post reply stating the pump could be at fault for the rads problem.

What motorised valves do you have on your system?

 

[ASDAW]

There is a Landis & Staefa metal box located at a T position on the pipework next to the hot water cylinder. There is a power cable to it.
I assume this is a motorised valve. It has a paddle position indicator A or B which is difficult to see due to the location I think it is on B. Underneath there is a lever which has an arrow saying MAN open.

 

[mogget]

There is a Landis & Staefa metal box located at a T position on the pipework next to the hot water cylinder... I assume this is a motorised valve.

This is indeed a motorised valve. Assuming the system was working properly before, it sounds as if the valve is sticking and not motoring over to the CH position. This could explain both faults.

Could you try this?

- lock the valve in the open position with the manual lever

- fire the boiler for 15mins or so in HW mode (may need to turn the cylinder stat up to make sure it doesn't shut off)

- let us know whether your radiators get hot.

 

[ASDAW]

I locked the valve as you said (with both HW and CH selected) then I could instantly here water moving through the valve - the radiators then got hot. The heating then seemed to be working fine.
Thanks very much for this. Is it sticking intemittently ?

However, I have just tried to change a room stat which had a faulty control knob which wouldn't locate. I could not get the room stat to fire up the boiler at all.
It is on of the ones where the wiring is on a back plate and the front of the stat has locating pins which enter holes at the connections.
As I couldn't get the stat to work. I had the power on with the back plate not fastened to the wall so I could check if the pins were locating. I have put the old stat back on but now when I try and select HW or CH from the controller there is no 'click' as it switches on and the boiler will not light. There is power to the controller though.
Have I blown something in the controller?
Sorry about this I know I should leave these things to the professionals.

 

[mogget]

OK, best to check the control system before paying out for a new valve.

You'll need a multimeter - a neon screwdriver isn't reliable.

If the wiring is the same as the honeywell 3 port valve you should have five wires.

Green / yellow - earth

Blue - neutral

White - this should be at 240v when heating on and room stat / programmer calling for heat, 0v otherwise

Grey - Should be 240v when hot water turned off or cylinder thermostat satisfied, 0v when hot water is being heated.

Orange - this is the tricky one, with the valve connected should be 240v when either heating or hot water calling for heat, 0v otherwise. This connection is powered directly from the cylinder stat when hot water or hot water AND heating calling, and through a microswitch in the valve when heating ONLY is calling. In any case the switched live for the boiler is connected to this terminal.

Have a check through, as long as you can be safe with electrics - let us know the results.

 

[ASDAW]

Thanks Mogget for your swift replies

Any thoughts on my other problem?

 

[mogget]

Do you mean the rads only warming up upstairs, and not down?

 

[ASDAW]

no I meant the post at 352pm
I have sorted that now it was a blown 5A fuse - you might not have seen the latter part of my post - ta

 

[mogget]

Is everything working properly now ?

 

[ASDAW]

for the moment all is well
rads up and down all hot and hot water OK, boiler firing on either or both
This has happened before though - due you think it might be the valve just sticking occasionally and opening it manually has freed it off?

I will keep you posted Mogget thanks

 

[mogget]

Yes, it does sound like a sticking valve.

Incidentally it's common for the hot water circuit to be in 22mm pipe with no balancing valve. This can cause problems when heating+hot water together is selected, because the (low-resistance) hot water circuit can 'steal' water from the radiator circuit. When heating alone is selected the hot water circuit is closed off and doesn't cause a problem.

If there's no balancing valve on the hot water, when you change the 3 port valve, put an ordinary 22mm gate valve in the hot water circuit, set it nearly closed and take the wheel off so it can't be tampered with.

Lastly, if you drain the system don't forget to add inhibitor when you refill it (it may sound obvious, but people do forget).

 

[ASDAW]

top info thanks loads for your time

 

[mogget]

No problem, glad to be of help.