Divertor Valve/Thermostat Problem

[brbrown]

I have a Gas Board heating and hot water system which uses a Glow Worm boiler with a Honeywell room and cylinder stat, Randall time clock, Honeywell three way motorised diverter valve and WSP pump.
When the time clock is set to "time" or "constant" with the room stat calling for heat, the diverter valve used to switch over to heat the rads as soon as the hot water cylinder reached temperature.
Suddenly the valve would not switch over so I first replaced the valve believing it to be faulty, then the stat which has made no difference. If I use the valve "manual" override lever, the rads will heat.
Can anyone please tell me what else could have gone wrong?

 

[Slugbabydotcom]

Assuming you have replaced the motorised valve correctly and that a wire hasn't come loose, there's only two items left to replace. The programmer and the cylinder stat.

With a correct call for heating the white wire leading to your motorised valve should go live.

 

[brbrown]

That's where a puzzle comes in because, when I set the room stat to call for heat, the boiler comes on and indicates this on the stat display but does not switch the valve over. Also if I turn the boiler stat temperature down, the boiler goes off. If I turn the cistern stat temperature down, the boiler goes off. It seems to me then that they are working. What else can be wrong. All the wires are back as they were?

 

[D_Hailsham]

the diverter valve used to switch over to heat the rads as soon as the hot water cylinder reached temperature.

So you couldn't have cylinder and radiators heating at the same time?

Do you still have the old motorized valve? If so, what is the model number or the number on the actuator - that's the metal box on the top.

What's the number of the new valve?

 

[brbrown]

Hello. I believe the system heats the water cylinder first, then when up to temperature, the valve switches over to the heating (if the room stat is calling for heat). If I did not want to wait for the cylinder to heat, I could always move the lever on the valve to bypass and the heating would function first. I can still do this but it will not swap over automatically like it used to. Consequently, I can't leave the system on the timer when I am not at home and have both hot water and heating when I arrive home.
The old valve was a Honeywell 40002826-002 and the new one advised by Honeywell as the equivelent is V4044C1288.

 

[D_Hailsham]

You have a Hot Water Priority system, aka 'C Plan'. If you want to be able to have HW on at the same time as the CH, without manually moving the valve lever, you will have to convert it to a 'Y-Plan' system.

Depending on which timer/programmer you have, this may involve just changing the head of your valve and some wiring alterations.

Here are the wiring diagrams of the Y-plan (left) and C-plan (right):

View media item 70 View media item 73

 

[brbrown]

Thank you for the information. I don't wish to change the system from the way it worked before. I'ts just that I the valve will no longer switch over to heating when the cylinder has reached the preset temperature. I have however just discovered that if I turn the cylinder stat to a slightly lower temperature, the valve will switch over. Perhaps therefore, the cylinder stat is faulty.

 

[D_Hailsham]

Either the cylinder stat is faulty or the water is unable to reach the temperature set on the stat.

What temperature is the boiler set to? It needs to be higher than the cylinder stat as the cylinder water can never get hotter than the boiler.

 

[ianmcd]

yes check what you have your boiler thermostat set to as it needs to be higher than what you have your hot water cylinder stat set at or the cylinder will never get hot enough

 

[45yearsagasman]

I may be wrong, but surely that wouldn't that have been an old W plan system with HW priority?

 

[brbrown]

Thank you all for the replies. In the past I have always had both the boiler and cylinder stats set to 140 which has always appeared to work satisfactorily but things seem to be working now with the boiler set at 130 and the cylinder at 120 which bears out what you say.If it wont work at the higher temperature, could it be that contacts inside are dirty or corroded? I suppose that could be classed as faulty.

 

[45yearsagasman]

Duplicate

 

[45yearsagasman]

Duplicate

 

[45yearsagasman]

The boiler stat should always be set higher than the cyl stat. Try 130 on the cyl and 150 on the boiler if you are not satisfied with water at 120.

 

[45yearsagasman]

Duplicated post