Boiler not able to run on CH only

Joined
1 Jan 2006
Messages
122
Reaction score
0
Location
Hertfordshire
Country
United Kingdom
Hi

I've got an old Glowworm Energy Saver boiler that is playing up. The timer unit only allows me to select HW and CH together or HW on it's own. When I put it on HW and CH together it runs fine until the cylinder water is hot enough, the thermostat on the cylinder instructs the boiler to run in CH only and the boiler then clunks a bit. the pipes/rads bang and the bolier cuts out. I then have to push the reset button to get it started again but it only lasts a few minutes before cutting out again.

If I use a lot of hot water or wait until the water is cold then the boiler works fine until I get in the situation described above.

I've found a Honeywell motorised valve with an AUTO or MAN ON setting and it's currently set closer to MAN ON than AUTO. When the cylinder thermostat kicks in I hear a click in the valve but very little else and the bolier then cuts out.

The arm on the valve freely moves between AUTO and MAN ON when I move it - there is no resistance which I understand may be a problem but is this also what is causing the boiler to cut out? Would setting this valve to either setting sort out my CH problem?

Currently we can only have the rads on if there is no hot water.

Any advice or tips is much appreciated.

Cheers
 
Sponsored Links
You appear to have a C Plan.

The lever will be loose when the valve is open, ie when the cylinder is heating up. Does it get harder to move when the system is turned off or the cylinder stat turned to minimum. If so, the valve is not sticking.

The problem is then due to the the internal changeover switch in the valve. This keeps the boiler running when the valve is open and closed. Here's the wiring diagram:


(Click to enlarge; right click to save)
View media item 73
When HW only is required valve is opened by the brown wire connected to the cylinder stat and the boiler is turned on by power from the grey wire via the valve switch and orange wire to the boiler. If CH is required the valve switch is also supplied by the white wire from the room thermostat. The boiler will be supplied from either white or grey wires, depending on whether the cylinder needs heating.

You say that the timer only allows HW by itself, or HW and CH. The C plan does allow HW and CH to be controlled completely separately, so either the timer is incorrectly set or just not compatible with C Plan. Which timer do you have?
 
Energy saver installed on a C plan Mr Hailsham????? ;)
 
The system is now off and the valve lever is just as loose as before.

The timer is a Pottertron EP2000. It has 2 black switches - one for CH and one for HW. I can slide the HW one independantly of the CH but when I slide the CH it slides the HW one too.
 
Sponsored Links
Energy saver installed on a C plan Mr Hailsham?????
:oops: Didn't notice it was an Energy Saver.

So we have a fully pumped system with a timer configured for a C Plan.

The OP only mentions one valve, so we seem to have a Y plan.

The system is now off and the level is just as loose as before.
Is that off at the timer or at the main wall switch/fused spur?

If off at the main switch/spur, the valve is sticking open.

If just turned off at the timer, turn off at main switch and check again.

Is the valve sticking when power off at main switch?

There is a switch (10/16) on the back of the EP2000; it is probably in the 10 position. Move it to 16 and you will be able to have heating without hot water (when the valve problem has been resolved).
 
Sorry, that was off at the timer. I just turned off at the main spur and yes, the valve lever gives a bit of resistance when moved from AUTO to MAN OPEN. Without locking it in place, it moves back towards AUTO (not all the way mind, about 2/3 of the way).

I checked the back of the timer and yes, the switch is in the 10 position.

We've only recently moved in and I did get a plumber to advise how the system works when we first moved in and he mentioned a gravity fed system. I'm no expert but there is a pump though I'm not sure if it's fully pumped.

I'm not blaming the plumber for not spotting this (yet) as everything was and does work fine for a while until the water gets hot enough - it's not apparent straight away.

Either way, I'm still unable to run the CH when the HW hits the thermostat temperature.

Anything else I can test or suspect as being the problem?

Cheers
 
Sorry, that was off at the timer. I just turned off at the main spur and yes, the valve lever gives a bit of resistance when moved from AUTO to MAN OPEN. Without locking it in place, it moves back towards AUTO (not all the way mind, about 2/3 of the way).
Now we're getting somewhere. ;) The valve is not sticking.

I'm still unable to run the CH when the HW hits the thermostat temperature.
If you then turn the HW stat up, does the boiler come on?

If it does, there is a wiring problem.

How many wires connected to the cylinder stat? There should be three.
 
Sometimes when I turn the HW stat up the boiler does come on, yes. But, sometimes I have to go down and push the reset button on the underside of the boiler to get it going. I'm not sure what is causing the reset button to pop out but it seems to depend on how bad the banging and cluncking is when it cuts out. There's been the odd time when the expansion tank overflows too at this point.

There is one cable from the stat with 3 wires inside. This goes down to a junction box in the garage (where the valve is) and off of this junction box there is one cable to the valve and two cables into the boiler area (I can't see exactly where these two go). Each of these cables is made up of about 2 or 3 wires but the junction box is a bit messy to see what is connected to what.

Hope this helps.

Cheers
 
sometimes I have to go down and push the reset button on the underside of the boiler to get it going. I'm not sure what is causing the reset button to pop out but it seems to depend on how bad the banging and cluncking is when it cuts out. There's been the odd time when the expansion tank overflows too at this point.
The reset pops out if the boiler is overheating (banging and clunking). That can be caused by a faulty pump or a blockage.

Use a screwdriver as a stethoscope and you can hear if the pump is running or not.

The blockage may be in the boiler's heat exchanger, but more likely at the junction of the cold feed (15mm) into the pipe from boiler to pump. Use a magnet to check the pipes at the junction. The magnet will stick to the pipe if there is a blockage.

It's probably time to call in a heating repair man. :(
 
Got a plumber coming but I've just been thinking about this a bit more. I checked the pump and it seems to be running ok. It has 3 speeds and is set on the middle speed.

If it is indeed a blockage, then this only happens when the system tries to run on CH only. If I empty all hot water from the cylinder tank and fire up the boiler, everything works fine for ages. Once the cylinder water is hot enough, the thermostat indicates to the boiler to do CH only and pretty much immediately I hear a straining downstairs (could be boiler/pump/valve) and then the systems shuts down. If it was a blockage it only seems to happen when trying to run on CH only. It's fine when running CH and HW. Depending on how cold the cylinder water is I can sometimes get a good hours usage out of the boiler to heat up the rads and cylinder before the cylinder thermostat kicks in and I lose all use of the boiler.

Definitely a blockage??
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top