Hi, I was wondering if anyone could help me. I have a conventional boiler with a large storage tank. I have two swiches on the system -- one for hot water the other hot water/ central heating.
When I press "hotwater/central heating", the radiators only seem to heat up for a short burst then go off and never come back on. Meanwhile the water heats up and the radiators never seem to come back on. If I then use a large amount of hot water by having a bath, the radiators will start becoming hot again. Is this normal. I fear that there is a problem with the valve? Can anyone help explain in very simple terms. Many thanks. Will.
Are you referring to a motorised valve? If so, how many are there in the system, and what type? [Clue: There is likely to be either one 3-port valve or two 2-port valves]
If you describe the system more fully, we can tell you what to look for. However, it's pretty obvious that the CH is only coming one while the HW is being heated, and goes off as soon as the HW demand is satisfied. This is very likely a problem with a motorised valve, unless it's always been like it - in which case it could simply be wired wrongly.
hi Roger, thanks very much for replying and your explanation.
I have just checked the system and have a motorized valve. It's pretty old, I think -- a sundial y plan 3 position diverter valve. I think it's been here for about 20-30 years -- do they often break down? Are they easy/ cheap to repair, or is it best to get an electrician in?
It's unusual for them to last as long as 20 years!
The valve is in two parts - the wet bit which directs the water to the HW or CH circuit or both together, and the actuator (the electrical bit which rotates the paddle in the wet bit to make it do its business. With many valves, you can replace the actuator without getting wet - but if you've got an early Honeywell valve you may not be able to do this.
Several things can go wrong with these valves. The wet part of the valve can seize up such that the actuator's rather weedy motor and return spring can no longer move it. The motor and/or the microswitches in the actuator can fail.
Before attacking the valve, it would be as well to check the wiring very carefully to make sure that nothing has come adrift. You can find a wiring diagram by looking under 'Y-Plan' in
formatting link
feature of Y-Plan systems is that there needs to be a positive signal to indicate that the HW demand is satisfied (or not required) - because that's what drives the boiler and pump in CH-only mode. So your programmer must have a HW-off output which is live when HW is switched off, and is connected to Pin 7 in the wiring centre. Likewise, the cylinder stat must have a change-over switch (rather than a pure on/off) which switches the HW signal from the programmer either to Pin 8 when the HW is being heated or to Pin 7 once the tank is hot. In CH-only mode, a microswitch inside the 3-port valve's actuator connects the grey and orange wires together - thus using the feed from Pin 7 to power the boiler and pump via Pin 8.
In your case, the feed isn't getting to Pin 8 for some reason. This could be due to:
a wiring fault
a cylinder thermostat problem or
a 3-port valve/actuator problem
If you are competent with a mains voltmeter (forget neon screwdrivers!) you should be able to work out where the problem lies.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.