boiler cycling every 2 mins

[Agile]

Because heating system controls work on electricity many people call an electrician although in fact few electricians can even wire them up let alone fault find on them.

Next they call a plumber, however most plumbers work on plumbing and have little knowledge of controls.

The only trade which specialise in boiler and heating controls are those who call themselves "boiler engineers" or "heating engineers". Even so some faults are still difficult for them to find and for those someone with an electronics background is required.

Tony Glazier

 

[croydoncorgi]

If the zone valves are Honeywell it would be unusual (but not impossible) for one to stick so far open that the switch is operated. The more usual scenario is the valve stuck at the 'nearly fully open' position, but failing to work the switch (and therefore the boiler, pump, etc.).
But lookalikes such as the Siemens zone valve operate mechanically AND electrically simultaneously, and DO stick electrically.

If the boiler is DEFINITELY cycling when there is NO call for heat, as a heating engineer (!) my first port of call would be a wiring problem.

 

[peterm1]

Had a call from the sparky to say that he has spoke to the gas engineer he is working with about the 2 min cycle on the heating side, and they seem to think that the pump is not taking the hot water away quick enough (up three floors).The reason it does not cycle every 2 mins on the water is that it only travels a short distance( almost side by side to the boiler).I have checked the pump which is running on 3 setting ok,2 setting ok, but on 1 it is not running at all.

 

[scatmanjohn]

Had a call from the sparky to say that he has spoke to the gas engineer he is working with about the 2 min cycle on the heating side, and they seem to think that the pump is not taking the hot water away quick enough (up three floors).The reason it does not cycle every 2 mins on the water is that it only travels a short distance( almost side by side to the boiler).I have checked the pump which is running on 3 setting ok,2 setting ok, but on 1 it is not running at all.

What?????

I thought you said that the boiler was firing up and cycling every 2 mins even when there is no demand.
By no demand we mean the programmer is turned to the OFF position for both heating and hot water.
Is this the case?????

 

[peterm1]

The sparky found that the programmer on the heating so we replaced and that stopped the bypassing,but we are still cycling every 2 mins when desired temperature reached.Do you think there could be a big airlock on the heating system>

 

[jobloggs]

MY system is a pegler but I assume that they are all much the same.

What should happen is that both valves are closed when when stats are satisfied and if valves are both working properly no power should be getting to the pump/boiler. But it is, so the problem is one or more faulty valves either:
(a)sticking open or
(b)closing but with the microswitch staying on.

Short Cycling is because a small volume of water is going thru the bypass, heating up and cooling down quickly and activating the boiler stat. Check that the pump goes on and off along with the boiler or does only the boiler cycle.

However if the problem is happening when the programmer is off this suggests another possibility. In this case there should be no live feed from the programmer to the wiring centre with HW off and CH off. However when wired for a 3 port valve (Y plan) there is a live feed from programmer to wiring centre. Check by removing programmer from its backplate. There should be only two of the 4 numbered terminals with wires. (There are differences in the way a tank stat is wired in for the two plans as well. In Y plan it sends a live signal back when satisfied as well as when it is demanding (3 wires instead of 2) ).

Did your electrician have a s plan wiring diagram in his hand when he was looking at the problem? If not I wouldn't expect him to remember all the wiring details.

The only doubt I would have about this being a wiring problem is that it appears to have developed suddenly and wiring if correct at the start does not tend to change on its own.

Excuse these rambling if I have stated the obvious or repeated points already made by others but I'm just trying to think my way logically thru the problem rather than having any experience.

Someone once said that if you eliminate all the possibilities then the impossibity you are left with is the solution.

 

[peterm1]

The new programmer has now stopped the bypassing.
The water is now cycling every 2mins until it reaches temperature,then it shuts down and performs normally(say heats up only when required.
The heating however, once it reaches temperature shuts down and continues to cycle every 2 mins indefinately.