Help needed, refilled central heating system not working!...

[shorn]

Hi all, looking for a bit of help or advice.
Last Friday my central heating stopped working. I have a standard vented system with a quite old boiler (Radiation Fuelsaver 9), and feed and expansion tank in the loft.
I managed to get a plumber who's a friend of a friend, (works for BG) to come out. After looking over the system he said that it appears to be the 3 port mid position valve. He set it to the locked open position, and for the past few days we have had a bit of heating, only when the hot water was being called for. (i.e. when the hot cylinder was filling the pump would kick in and boiler would fire up, but once the hot water was satisfied it would then cut out.)
So I set about today to replace the valve. I drained the system, (a bit harder than expected due to a wedged drain cock), but eventually the system was completely drained. I replaced the valve. (it was a like for like replacement) everything went back , all fine. I then untied the ballcock in the header tank and started to refill the system, this seemed to take an age, but eventually it refilled, bled downstairs rads first, then upstairs, shortly after the header tank finished filling.

So far so good!

Switched the power back on to the central heating. Now when the CH only is selected, the pump would fail to kick in. When the HW was selected it would go.

Downstairs I went down and turnt the boiler on, lit the pilot and then on, it fired up.

Now 10-15minutes later, the boiler has gone out. I've tried relighting, I get a pilot when i hold the ignition in, but it will not stay lit.

So a couple of questions really! Why does the pump not kick in for CH only? and is there any suggestions as to why the boiler is not now lighting?

If I need to clarify anything further please ask!

Really hope I can get some help, I would normally let someone more qualified do this type of job, but the earliest we could get someone out was beginning of next week, which was just too long as we have a one year old and the house is gradually getting colder and colder!

Thanks!

 

[D_Hailsham]

So I set about today to replace the valve. I drained the system, (a bit harder than expected due to a wedged drain cock), but eventually the system was completely drained. I replaced the valve. (it was a like for like replacement) everything went back , all fine.

Did you get the valve the correct way round? Port A goes to the rads, Port B to the cylinder.

I then untied the ballcock in the header tank and started to refill the system, this seemed to take an age, but eventually it refilled, bled downstairs rads first, then upstairs, shortly after the header tank finished filling.

Did you lock the valve in the MAN position while refilling?

Switched the power back on to the central heating. Now when the CH only is selected, the pump would fail to kick in. When the HW was selected it would go.

What tests did you carry out before assuming that the valve was faulty?

Are you sure the valve has been wired correctly?

Did you follow the instructions for lighting the pilot?

 

[MANDATE]

First thought is when refilling did you latch the lever in the mid position.
This is required so water can pass through both ports, otherwise you're liable to create a 'air lock'. Other than for refilling the lever should be left unlatched (auto mode).
The mid position valve is not easy to understand.
It works over two sections from its rest position (HW)
To get to mid position the room stat has to provide power to the white wire of the valve.where it feeds two micro switches
At midposition one micro switch is triggered which cuts off power that was driving motor and cuts in power supplied by the 'grey' wire so the motor can continue to the CH position. This of course depends if the grey wire is live, if its not then the valve stays at mid position.
So first question would be, does valve move from HW and beyond mid position to CH position. If not I'd suspect incorrect wiring.
Why not turn both HW and CH off and test the 'grey' going into valve. this should be live. It should not be live when HW is on and in demand, or when both HW and CH are on and in demand.
The other thing to remember is power to light boiler comes from the cylinder stat except when CH only is on and in demand. In this situation power is supplied from the valves orange wire.

 

[shorn]

OK, to answer a few of the questions. I have replaced the Valve on the recommendation of the plumber that had a look at it, (a British Gas engineer.)

The valve was a ACL Lifestyle 679340-30L0 valve and I have replaced with a Drayton MA1/679-3 (22mm). This was a direct like for like replacement. Same wiring, same structure and dimensions. The new one went in the exact same way the old one came out, I even went through wire by wire. When I installed it, The manual lever was locked in so that the valve was in mid position. Once the system was refilled, I did unlatch it to auto. When I turn CH off I can hear (and feel) the lever moving, so I am assuming it is doing its job. I will have a check in a moment where its actually moving to.

Im not sure what you mean by test the grey, do you mean just test to see if it is live?

Followed instruction for lighting pilot, as per the inside of the casing.

Would a pic of the junction box help?

 

[shorn]

The one other thing that has been a bit strange lately, is that our room stat starting showing a battery sign (its a Honeywell T6620B) on its digital display, I replaced them with energiser rechargeable, (2450mah) and I noticed that the battery light is on again today, which means that it lasted about 4 days. That does not seem right surely? I assume this would not have an effect on things? I mentioned this to the plumber, and he tested by making a direct connection at the room stat and I was still having the same problems.

 

[slup]

Rechargeable batteries are 1.2V not 1.5V so even when fully charged, they will look to be low to your thermostat.

Stick a pair of alkaline batteries in there.

 

[shorn]

Ahh makes sense will do.

Just been and had a look to see where the valve is moving, and this time it didnt seem to move anywhere, the manual lever is unlocked in auto, but switching between HW only, HOW and CH, and CH only, didnt result in it moving at all ? Do you think its faulty.

Decided to check the wiring,

The wiring for the valve seems fine. However!... when i was inspecting it, I noticed a wire that is not connected to anything.

If you look in the photo, you will see two cables that come down from the programmer, the one on the left has two brown, two blue, one earth, and one black, which you can see just by the 8/9 position. The cable connecting to 9 & 10 is the other from the programmer.

 

[D_Hailsham]

How a mid-position valve works contains full fault finding information.

 

[shorn]

Thanks for the link.

I check turnt the power off to the valve to let it reset and tried again. This time it would sit on HW only, move to the mid position when HW and CH is called for but would not move to just CH. SO using the guide I connected the grey and white to live, turnt back on and it moved to CH only, and the pump has kicked in. This is obviously good, however the boiler is still not lighting.
PIlot light will not stay on. I can see the pilot when I hold the control knob in, and ignite it, but it does not stay lit. In teh guide it says Switch S2 is not moving over. Not sure what that implies?

 

[shorn]

Anymore takers on this one? I've traced the black wire back up to the programmer and its connected to To the HW OFF terminal. That same cable has an earth, Brown to Live and Blue to Neutral. (The other cable has Red HW On connected to 10, (Which is HW on) and Black CH On, which is connected to 09 (Which is CH On)

Now from how the wire is sat it looks as though its come out of 8. and in the junction box cover it states that this is HW OFF (But that is in the section for the valve.

As per below...

Really need some help if at all possible! Thanks!

 

[Hugh Jaleak]

Good 'Y' plan wiring explanation here: http://octaveblue.co.uk/c_heating/index.htm Might be as well to check everything is connected as it should be.

Boiler not lighting, this sounds like a seperate issue. You'll need a Gassafe engineer to deal with this, but from your description it should be a reasonably quick repair.

 

[shorn]

I'm getting somewhere!

OK, looked at those diagrams, checked all wiring again, and then connected in the black wire to "8".

Fired it up and the actuator and the valve seemed to be operating as they should be. I can now run it on CH only, HW only and CH & HW, and I can see the actuator pin moving properly to each location. Good stuff.

However! Boiler still refusing to ignite. This seems crazy as it lit a few hours ago, when I turned the system back on. What could have possibly gone wrong with it? If the boiler would fire then i'd be all up and running!

Any thoughts as to what could have happened? As i said When I hold the Control knob in, and then Press the ignite button, the pilot lights. I keep it held in for 20 secs + and it goes out.

 

[shorn]

Success!

Read a few things online about standard boilers, and my problem pointed to the thermocouple. Was encouraged by the fact that these can be replaced, so I checked it over. When looking at the boiler I noticed a very non descript green pin right down the back left hand side. I pushed this in and it seems to have reset it! Boiler fired and heating has been on all night!

Thanks for the help all!