Oil boiler running on when no demand

[Markcoopers]

Hello,

First post and I hope the collective wisdom here can help me.

I have an older Euro Cal oil fired boiler connected to a pressured hot water tank and the heating with each rad having a stat attached and the boiler having a digital clock for water and heating.
The system uses a 2 way Honeywell (silver box on the valve head) for the hot water control and a 2 way Drayton ZA6 valve (white box) for the central heating.

Of late the boiler has continued to remain on and the circulation pump stay on even though the clocks have all switched off. I assumed this was a overheat safety think, but no lamps on the boiler were lit indicating this, other than the normal green "on" one. Indeed if I turned the boiler stat down the boiler would stop firing but the pump and the boiler were still active. the valves were shut though and the pump was caveatting.

If I manually then turn the system on again I can hear the valves so as to push water through the system, then turn all demand off again it will after a few minuets all switch off. Sometimes needing a few repeat attempts of this. This is why I thought it was a over heat safety thing, and think perhaps one of the Thermisters on the boiler is at fault or the boiler itself.

However I have noticed that while the boiler and pump are doing this running on thing, all clocks and demand off, if I manually push the Drayton zone actuator lever to the open B position the system will then fully switch off after a few seconds.
At rest (cold) this zone valve also only seems to be halfway between the A-B position and I can not close it any more to the full A position.

Any ideas, new actuator to solve a sticking or stuck or faulty microswitch or is this more of a boiler issue?

thank you.

 

[Terrywookfit]

It could be the valve spindle sticking in the drayton. Remove the head when it is faulty, the valve will probably then close and stop the boiler and pump.

 

[Markcoopers]

Good idea. I removed it now and was able to get the little black lever fully out and the indicator back fully to A. I shall wait it playing merry tonight at 10.30 and then try the removing of the head to see if it then goes back and what it does.

 

[Terrywookfit]

Good idea. I removed it now and was able to get the little black lever fully out and the indicator back fully to A. I shall wait it playing merry tonight at 10.30 and then try the removing of the head to see if it then goes back and what it does.

It is a common problem. There is usually signs of leakage on the spindle where it comes out of the brass body.

 

[Markcoopers]

No leakage, but the more I think about it I think it is the microswitch in the Dayton unit. I wonder if it is sticking on, and me manually pushing the valve to open and releasing it is releasing the micro switch. I will pay more attention to what actually happens when tonight. after all me manually opening the value turns the micro switch on and if I do it now with the system fully off I can here the pump start......the opposite to what happens when I shut the system down.

 

[Terrywookfit]

The manual lever is only for system filling. The microswitch will only engage momentarily by using the lever.
The motor drives it past this position to engage the switch.

 

[Markcoopers]

Also I have to ask, is that Viz comic reference?

 

[Rodders53]

I've had the microswitch stick closed on in a Drayton/British Gas/other ZA5 type unit - on the late in-Laws system.
It was a mechanical issue on the plastic microswitch button actuator; but will probably after cleaning etc.,. repeat the same 'stuck on' fault.

I got a replacement switch and soldered it in rather than a new head (me, tight? too right!). You'll need the part number off the microswitch housing if you want to do that. It was a slightly difficult find - but eBay item 153922425244 looks the right part.

 

[Markcoopers]

Thank you all.

I opens up the junction box to find that the white wire on the Za6 was just terminated safe, so purchased a Za5. Wired in and all working properly.

I took the old unit to bits, the black plastic bits had worn meaning that when the motor switched off and returned it stopped half way but the micro switch was still operating.