Heating problem

[wisey]

As an update for you on this, we have had the programmer changed as thought this was the most likely cause but no luck. Still having problem.
Plumber is coming round monday to have a look at PCB and Room Therm, as he says that these are the only things left he can replace.

Reminder of Problem - Heating set to come on at 5 am. Comes on for approx 1 hour then turns off, regardless of temperature on RT. If you change programmer setting to off and then put on to constant setting, heating works fine and comes on and off as called by the RT. (I was wondering if something is telling boiler to turn off once water has reached temp as that would take about an hour wouldn't it ??)

This is really puzzling everyone and we even had a spark to have a look but he couldn't identify any issues either. Will let you know in the PCB and Thermo changes make any difference, unless anyone has any other ideas as what it may be.

Thanks for all your responses so far.

 

[MANDATE]

I looked at problem recently that was fairly similar. No problem at morning but no heating later in day.
The system was set for both HW and CH to come on at morning, so motorised valve went to mid position and everything seemed OK.
The use of hot water in the morning and replacing it with cold water helped to keep the system running, but when the cylinder stat was satisfied, the motorised valve moved to CH position as it should, but the system closed down because there was no longer a feed to the boiler/pump through the orange wire.
If hot water was run off then the valve returned to mid position again and boiler/pump was activated supplying water to both the cylinder and the heating.
A check on the orange wire when on CH only show there was no voltage, even though the valve was in the correct position.
If HW is required (either only or shared) the feed to the boiler comes direct from the cylinder stat
The actual fault was traced to one of the micro switches in the motorised valve so it could not feed the boiler pump.So no heating without hot water. A replacement actuator head cured the problem.

 

[wisey]

Had the bioler installer out last week and he said boiler looked ok (only 7 mnths old) but advised me to, next time it wasn't working, put an electricians screwdriver on the 'Switched Live' wire to see if there was power. If lighted up means boiler issue if not, external issue. Tried this and screwdriver lit but very dimly.

Spoke to boiler bloke again and he says this sounds like low power being sent to boiler causing it to turn off. He is coming round tomorrow with a volt meter to test this and try to trace the problem.

Does these sound feasible and if so any ideas what the likely cause of low power may be (dodgy Room Therm - this is the only trhing that isn't new ?), so I can offer him any help.

Cheers guys

 

[MANDATE]

Room stat or motorised valve?
It's easy to check the room stat with your electricians screw driver. It's just a switch, so you have a live wire going to the switch and the wire coming out will only become live when you turn the stat up to call for heat. The wire coming out will go to a wiring box usually with 10 terminals.
The terminal that contains the 'white' wire from the motorised valve will also have the wire from the room stat, so it can be checked at this point.
You could do with checking the motorised valve to see if moves from 'HW only' to 'mid position' and 'CH only' according to what you select.
If it does move to CH only, you can also check the wiring box terminal to see if the 'orange' wire is live.
If the micro switch is dodgy with dirty or burned contacts, that may account for your dim light on your screwdriver. only problem is that you can't easily repair or replace the micro switch.
Best thing is to invest in a multimeter and measure the voltage, maplins do one for less than £5.

 

[wisey]

Thanks Mandate.

The plumber is coming out again tomorrow and bringing a multimeter with him to try and track this fault so hopefully we will resolve the matter once and for all.

You say the micro switch is difficult to replace/repair - does this go for people that know what they are doing or just incompetent muppets like me. Where is the switch and what makes it dirty ?

The only reason I mentioned it may be the RT is that this is the only thing that has not been replaced.

Steve

 

[ChrisR]

I tried to chnage one once and gave up! Sometimes they can be made to work by slight bending of metal which pushes the tit - people glue bits of card on etc. Normal answer is a new head, especially of the switch is sticking "Pushed".

 

[MANDATE]

Firstly there are two micro switches and on the valve I stripped down they were alongside each other and soldered to a small pcb, so it was impossible to remove the side of the faulty switch without desoldering and removing it. I did remove it and managed to dismantle it, clean it and re-assemble it and test it. So it does require some degree of skill, experience, understanding and luck but not neccessarily in that order.
When the contacts are continually making and breaking, arcing takes place and the contacts become burned just like the 'contact breaker set' on a older cars ignition. A slight build up of carbon will keep the contacts apart or cause resistance.

 

[wisey]

Had plumber back out this morning. Turns out that the original diverter valve we had replaced earlier this year was a copy of a Honeywell and not an original. Apparantely the motors in these are not as powerful and the problem we were having is that the motor was not turning enough to flip the micro switch. If you very lightly move the valve the whole system fires up.

New plumber is changing motor which he reckons will solve problem.

 

[planenut]

Phew!