Central Heating noise - when hot water switches on

[garysz]

In the morning, system is programmed to turn on CH and then 30 mins later HW comes on, both then run for another 30 mins.

When the programmer turns on the HW there is beteween 10-20 seconds of noise eminating from the pump / 3 way valve area. It is as if the pump is trying to pump against a closed valve. Then when the boiler turns itself on the noise stops and everything is OK.

What are the possible causes and solutions?

3 way valve is 9 months old, now all wiring connected via a fancy connection box. System has been drained sevearl times to remove air and rust inhibitors added on refil. Microbore system.

[Ed Sirett]

There is really little harm that will come to pump that is pumping against a closed circuit for a short while.

[Dave Plowman (News)]

Draining down a system and re-filling with fresh water actually adds air.

[Set Square]

Is the 3-port valve a diverter valve, as used with W-Plan systems - or a mid-position valve, as used with Y-Plan systems? [See

it's W-Plan, it can't heat HW and CH at the same time - and HW has priority, so it would make sense to programme HW to come on *before* the CH rather than *after* it.

It it's Y-Plan, I don't understand how the valve can ever be "closed" - because, AIUI, at least one outlet port is always open.

[garysz]

The valve has three positions on it, so it is a Y plan system?

I agree with your comment - the valve should not be closed and probably isn't. It merely sounds as if i is under effort and getting nowhere.

I forgot to add that this noise also occurs when I 'boost' the CH or HW on their own. The pump seems to pump, and thus makes a noise, until the boiler kicks in. Sometimes it can take 30 seconds for the boiler to respond sometimes it is more or less instant. Then when it does start all is fine. In this new connecor box could there be some sort of delay mechanism? Or is it incompatibility of components?

Thanks Garysz

[mike]

It sounds like a wiring error to me, from when the new connector was installed.

When the Ch stat sends a demand (or you boost it) this operates the valve that takes about 30 sec to operate. When it reaches the end of it's travel it closes a contact that calls the pump.

For HW, the demand for heat operates the pump and boiler directly.

If you go to

scroll down to Y plan, you will see that connector 8 on the block is made live by the cylinder stat from connector 6, and calls the pump and the boiler.

But the switched live from the room stat goes to the 3 pos valve, and then to the boiler and pump via the orange wire to call the pump and boiler, only when it's ready.

Your coneector numbers may well be different, but the circuit, and prolly the wiwring colours will be the same.

You may be able to suss it.

If you are checking for yourself, be sure to switch off the mains at the fusebox which should be close.

Lots of earthed copper + exposed live contacts may be fatal!

HTH

[Set Square]

If it has a mid-position which feeds CH and HW at the same time, yes.

If the valve is in the HW position, with HW satisfied or off, and with CH off - and you suddenly turn on or boost CH, the valve has to motor to at least the mid-position before it turns the boiler on - which takes a finite time. But it wouldn't run the pump during this period.

If the valve is in the mid or CH position when HW is boosted, the valve needs to move back to the HW position, using its spring return - but the boiler and pump should start immediately without waiting for the valve to move.

The only time the pump should run without the boiler firing is when the boiler is above the temperature set on its internal thermostat. This won't normally occur on startup unless the boiler has been running *very* recently, and is still at or above its stat setting. In that case, when you boost HW or CH, the boiler and pump will both get a 'go' command - but the boiler won't actually fire until some water has circulated through it for a while to cool it to below the stat setting.

I doubt whether there's any delay explicitly built into the control system. I suppose it's possible that there's a flow switch somewhere which has to detect a suitable level of flow before the boiler is allowed to fire - but that's not standard Y-Plan.