Lukwarm rads - and only when the hot water is on

[robmorgan]

Hi all,

Thanks in advance for any pointers on this.

Here's the prob:

- If I turn the CH on without the HW, nothing happens, i.e. the boiler doesn't fire, and the rads stay stone cold.

- If I turn on the CH with the HW, the upstairs rads get warm, one even gets quite hot, and all but one of the downstairs stay cold.

HW works fine on its own.

We're currently decorating from top to bottom, and so have removed, refitted and bled 3 of the rads - 2 downstairs, 1 upstairs.

Can't say if that's the cause of the problem as we only moved in in July and this is the first time we've tried to turn the CH on.

Boiler make/model: Stelrad Group Ideal W (Gas)

Many thanks,

Rob

 

[slippyr4]

what controls do you have? programmer? 3 port valve? 2x 2ports?

 

[robmorgan]

Urm... Timer is a Potterton EP 2000. Not sure on valves and ports, this is my first CH system! The boiler's got a dial on the front: OFF-1-2-3-4-5-6. Tried cranking this up from 5 to 6, with no joy. We don't have a room/wall thermostat.

Cheers,

Rob

 

[chrishutt]

You need to follow the main flow and return pipes from boiler to find the motorised valve(s) and tell us what you've got. Probably near the pump and hot water cylinder. The problem is likely to be with motorised valve switches, so you could check some of the threads on this.

 

[robmorgan]

Ok, think I'm with you. In the airing cupboard, next to the cylinder and pump, there are two boxes, both branded "Honeywell" with the code "V4043H1056".

I guess they've got two "ports" as there's a pipe going in and out of each.

They've got a switch on the top with two positions: "man open" and "auto".

Any ideas?

 

[slippyr4]

You need to work out which valve is which. One of the has pipes going to the HW cylinder, the other one goes to the rads, and that's the heating one.

Once you know which is the heating one, turn the CH on without the HW, and then slide the lever on the heating valve over to manual. Does your boiler fire?

 

[robmorgan]

No joy I'm afraid. There was a slight gurgling noise when I switched the valve, but the boiler doesn't fire.

There's some sort of junction/control box on the floor of the airing cupboard, looks a bit battered - any chance it could be malfunctioning?

 

[slippyr4]

I'll wait for Chris or someone else to comment. It sounds like either the motor or the microswitch in the CH valve is knackered, but I can't think of a particularly easy way to guide you into confirming that.

 

[robmorgan]

Thanks.

Even if the CH valve is kaput, shouldn't switching it to manual at lease get the boiler going?

Is the motor part of the valve?

 

[slippyr4]

the motor head is normally detachable. There's a microswitch inside too, which closes when the valve opens, which is wired to fire the boiler.

 

[chrishutt]

Even if the CH valve is kaput, shouldn't switching it to manual at lease get the boiler going?

No, switching to manual setting does not move valve spindle far enough to contact the microswitch.

It appears that the microswitch is not operating in the CH motorised valve. This would explain the symptoms you described. Ideally you would check that the grey wire to the motorised valve is live and that the orange wire does not become live when CH is run.

If this confirms switch problem, you should replace the head part of motorised valve, or even whole valve if the head doesn't seem to detach easily, unless you are good at electronics in which case you might try replacing microswitch.

A new motorised valve doesn't have to be Honeywell. Any 2 port with an auxiliary switch will do, for example Orkli (£20) brand from BES.

 

[robmorgan]

Thanks Chris, that's very helpful.

When I switch the CH on via the timer, should power always get to the valve/microswitch? Isn't there a thermostat in the circuit?

 

[chrishutt]

The brown wire that powers the motor that opens the valve will be linked through the room stat (for CH). However the grey wire is a permanent live and provides the microswitch with a live to connect to the orange wire, which feeds back to the boiler and pump. Go to the Honeywell site and look up S Plan.

 

[slippyr4]

The system is sort of isolated - and designed so that the boiler will never fire unless at least one valve is open.

 

[robmorgan]

We don't actually have a room stat, unless it's very well hidden! Is that unusual?

Is there not a thermostat in the boiler or switches themselves, that needs to open before any part of the CH will do it's job?

If the valve/switch is knackered, should the pump still start when I turn on CH without HW? It doesn't - currently only comes on with HW.