Heating Boiler Cycling up and down.

[john west]

Some months ago our Worcester green star boiler was replaced with a new Ideal logic heat 18 in a traditional set up with a hot water cylinder upstairs in a small terraced house.

After installation there was a problem with the pump working noisily all the time, never switching off.

The wiring was changed and this problem stopped. A new Grunfoss ups3 Pump was installed upstairs with a new EPH control and the system was drained and inhibitor added.

Now sometimes even though hot water and central heating are switched off at the Drayton lifestyle LP722 Programmer, the Boiler is still Firing up for no apparent reason.

It recycles from about 60 degrees up to about 80 degrees then switches off. Cools back down to 60 then switches on and up again to 80 in a

*Continuous Cycle*. It will do this for hours until i switch the Boiler Electrics off, from the switch just below the boiler.

Also when it is doing this the pump upstairs is on again continuously, at this time and seems to be making a lot more noise than usual.

The boiler is on the ground floor and the pump is immediately above it in the bedroom. Also whilst the pump is grinding away the copper pipes by the pump are very hot. But everything is still switched of at the programmer.

Grateful for any suggestions as to the possible cause of this recycling of the boiler with the pump continuously on. This is whilst all is switched off at the programmer. Thanks.

[Animal]

it's wired up wrong, or something failed.

[Roger Mills]

Does the system have 2 or more 2-port zone valves? If so, you have an S-Plan or S+ Plan system - one of whose modes of failure is just this.

The programmer and room stat and cylinder stat control the valves, and the valves in turn control the boiler and pump. Each valve has a micro-switch which closes when the valve is open. These switches are wired in parallel so that the boiler and pump run whenever one or more valve is open.

If a micro-switch fails closed, the boiler and pump will run, even if there is no demand from the stats. The pump will try to circulate the water but it has nowhere to go - other than the by-pass circuit - if the valves are closed, hence the pump is working harder and is noisier.

Under these circumstances, the pump will run continuously and the boiler will cycle on and off on its internal thermostat.

[john west]

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It has now taken to doing this 'sometimes' and sometimes not. A Neighbour has suggested it could be air in the system which might account for the pump being *very* noisy during the boiler recycling up and down ?

[Animal]

if it worked before, most likely dodgy switch/thermostat contacts Air is normally self solving

[Theo]

Air might cause it to be noisy, but I can't see how it would fire up unnecessarily (unless the valves are stuck somehow).

Is it a sealed system or an open one? If it's sealed there should be a pressure gauge - check the pressure is adequate. There should be a tap to allow more water into the system. If you have air release valves it will let air out, but won't let any water in without topping up via the tap.

If it's open there will be a filling and expansion tank (in the loft perhaps) - check it has water in it, and that the float valve is operating correctly.

Theo

[Animal]

Nah, if it's wasting energy cycling up & down get it a motorbike