Central Heating breakdown

My 10 year old gas CH system has gone on the blink.

The boiler fires up fine on the Hot water mode, but does nothing when I try run the CH. Any clues as to what this utter novice should attempt next TIA

Reply to
JP
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JP explained on 25/12/2006 :

If you have a two port valve, that being stuck would be the most likely cause. If it is an old type room thermostat, check that clicks over at the appropriate temperature. Check the time clock is showing on for heating.

Reply to
Harry Bloomfield

the damn thing has started working! Mystified but happy

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Reply to
JP

An awful lot depends on the design of the system, and exactly what components it has in it.

But, seeing as it's Christmas, I'll take a flyer and go for the most likely cause. I'm going to guess that you've got a fully pumped Y-Plan system with a 3-port mid-position motorised valve which directs the hot water from the boiler either to the indirect coil in the HW cylinder or to the radiators or to both at the same time. If I'm right, you have a problem with the valve - or more likely with the actuator (the electrical bit) - which is failing to move away from the HW position. Once the HW demand is satisfied, if the valve doesn't move to either the mid or CH position, the boiler won't come on because it's a microswitch in the actuator which actually switches it on. So, my diagnosis - starting with the most likely - but based on very little information(!) is:

  • failed motor in valve actuator, or
  • mechanical part of valve seized, or
  • faulty room stat - failing to relay the CH demand to the valve

Clearly, you'll have to sort out the valve and/or stat, but to get some heat in the meantime do the following:

  1. The valve should have a lever on it which enables it to be moved manually to the mid position. Operate the lever, and find a way of holding it in the manual position (string, tape, etc. if it doesn't have a mechanical latch)
  2. Turn the boiler stat down a bit to about 65 degC to prevent the DHW from getting too hot
  3. Turn the cylinder stat up to above 65 degC

The system will then run and will attempt to heat the HW to the cyl stat setting - which it won't be able to do - BUT the radiators will get hot - albeit not quite so hot as usual.

Reply to
Roger Mills

JP presented the following explanation :

Sticking valve it is then :-)

Reply to
Harry Bloomfield

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