Central heating only works for a couple of mins

[phoenix1589]

Hi all,

I have a typical hot water / central heating setup based on the Honeywell Sundial Y Plan - 2 Channel Programmer with mid-position valve and an old dial room thermostat.

The hot water is an unvented system, but I don't think this makes any difference for the problem I'm experiencing.

Until last week, everything with the system has been working fine. Since last week, the central heating is being very temperamental. When I turn it on sometimes the boiler starts straight away and other times it doesn't. If it does start, it is only on for a couple of minutes before stopping. After another 10 minutes, it may or may not come back on for a couple of minutes. The whole time, the programmer indicator light is on.

During this time, I have observed the radiators heating up (and then cooling down), so the heat is making it round the radiators when the boiler is on.

The dial thermostat has been turned to max. If I turn it down, I can hear the click, and then click again when I turn it back up.

Whilst the central heating is supposed to be on (but boiler not running), if I also turn on the hot water, the boiler instantly comes to life.

I have tried a different programmer, as I had a spare old 1 channel, and I see the exact same problem.

Does anyone have any suggestions what might be going wrong, or what I can try?

Cheers,
-Jeff

 

[phoenix1589]

As a follow-up, it sounds like it might be the 3-way valve being faulty (from Google research).

If I turn off the power to the system and move the manual lever, I can feel the resistance / hear the motor turning. However, this only starts from about 25-50% of the movement - i.e. the first bit of movement has no resitance, the last 50%ish I can hear/feel the resistance.

When I let got, the lever moves back a bit.

If I turn on the power and put on the heating and hot water, the exact same thing happens. The lever does not move freely.

If I put on the heating, and move the manual lever, the boiler clicks on for a moment, then off. Locking the lever in the manual position does not allow the boiler to run with just the heating turned on.

If I put the heating on and the boiler starts, the lever *does* move freely and I can leave it pulled towards manual (but not locked). Returning a couple of minutes later, the boiler has turned off and the lever has moved towards the normal position.

Based on this, I suspect it might be the synchron motor - however I can't explain why it sometimes works for a few minutes (unless it's almost dead but sometimes has a little bit of life!?). I'm also not sure if the first part of free movement from the manual lever is expected.

Anyone have any thoughts or comments on this?

 

[ALCPlumbing]

Feel the flow pipe at the boiler. Is it so hot that it's possible the boiler is overheating due to poor circulation. If so I would check the pump. Even if the pump is spinning it may be very weak.
Would also be helpful to know what boiler you have and whether any fault is indicated or if it displays the temperature what temperature does it show?