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Discuss Delay timer for heating pump in the Central Heating Forum area at PlumbersForums.net

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12
Excellent - I'll report back once I've wired the new stat into circuit next week!
Thanks, Graham
I've wired the capillary stat in now, and as predicted it seems to be doing the trick just pumping round the circuit formed by the ABV.

I've put the extra stat inside the boiler cabinet and brought an extra permanent live across from the main junction box to power the pump bypass. In fact I haven't actually wired it in permanently yet as it occurred to me that I now needed to isolate both my new permanent live to the boiler as well as the existing switched live. I'm using a three pole isolator switch for this (the sort that are used for timed fans) in place of the current switched, fused spur. The whole installation is already fused elsewhere in the room, so I don't think that losing this fuse local to the boiler is a problem - unless you advise otherwise! I could put a simple fused spur outlet in as well if thought to be needed.

Thanks again for all your help, and the interesting diversion about steam thermodynamics - I haven't seen some of those terms since I was studying Physics at school which was a very long time ago :)

Graham
 

SJB060685

Plumber
Messages
2,273
So the new stat wired into keeping the pump circulating after boiler shut down is pumping around that shirt 7m section of pipe and keeping the limit stat from tripping? If so that's handy to know that short length of run is enough for future reference.
Is the whole central heating circuit on its own 5 amp fuse and all wires come off that incoming supply?
 
Messages
12
Is the whole central heating circuit on its own 5 amp fuse and all wires come off that incoming supply?
Yes. Actually, I have a feeling that it's also on its own circuit from the consumer unit (probably with a 15A MCB but I'm not at home so would have to check that) as well as the local switched spur which powers all the heating circuitry.
 

SJB060685

Plumber
Messages
2,273
It could be on its own circuit and more often than not people will spur off a ring main. If its got a switched fused spur then it's fine and will protect the system componentsin the event of a problem. Oil should be on 5 amps but could be a 3 amp fuse in place.
 
Messages
12
It could be on its own circuit and more often than not people will spur off a ring main. If its got a switched fused spur then it's fine and will protect the system componentsin the event of a problem. Oil should be on 5 amps but could be a 3 amp fuse in place.
I wouldn't have been surprised if it was spurred off the ring, but I don't think it is. I'll check the fuse rating in the fused spur tonight. I presume that 5A for oil rather than 3A is due to the starting current of the burner motor.
Thanks, Graham
 

SJB060685

Plumber
Messages
2,273
I wouldn't have been surprised if it was spurred off the ring, but I don't think it is. I'll check the fuse rating in the fused spur tonight. I presume that 5A for oil rather than 3A is due to the starting current of the burner motor.
Thanks, Graham

The inrush current of the motor will be more than steady state yes. If its got a 3 amp in already and it's been fine until now then it should be fine, after all a 3 amp fuse should melt before a 5 amp in the event of a problem. I was just told on my OFTEC courses oil should always be 5 amp. If you really wanted to do the maths you could work out what current was being pulled but I've never bothered.
 
Messages
2,199
I've wired the capillary stat in now, and as predicted it seems to be doing the trick just pumping round the circuit formed by the ABV.

I've put the extra stat inside the boiler cabinet and brought an extra permanent live across from the main junction box to power the pump bypass. In fact I haven't actually wired it in permanently yet as it occurred to me that I now needed to isolate both my new permanent live to the boiler as well as the existing switched live. I'm using a three pole isolator switch for this (the sort that are used for timed fans) in place of the current switched, fused spur. The whole installation is already fused elsewhere in the room, so I don't think that losing this fuse local to the boiler is a problem - unless you advise otherwise! I could put a simple fused spur outlet in as well if thought to be needed.

Thanks again for all your help, and the interesting diversion about steam thermodynamics - I haven't seen some of those terms since I was studying Physics at school which was a very long time ago :)

Graham
What is the stat setting and does it cut in/out a number of times before the boiler temperature stabilizes?
 

ShaunCorbs

Staff member
S. Mod
Plumber
Gas Engineer
Messages
28,890
Solutions
1
Hi everyone,

got to the bottom of the wiring for this relay should anyone else do one.

perm live goes to A1 with link to 15
neutral = A2
switch live to S
pump feed on 18

thanks for everyones help

that’s an odd setup how did you figure it out ?
 

plumb_know

Plumber
Gas Engineer
Messages
534
spoke to couple of electricians and they both said they thought perm L should be on A1, then found these on geya website:



tested it on leaving sat morning and all seemed good & customer not contacted me since so seems to have resolved the issues
 
Messages
12
What is the stat setting and does it cut in/out a number of times before the boiler temperature stabilizes?
The stat is set to about 90C (I'll explain the about in a bit) - I couldn't decide whether it was better to have it come on sooner and "waste" electric running the pump, but nip the overheat in the bud so to speak, or set it high so the pump only comes on when there's a danger of the overheat trip going off. So 90 was a bit of a compromise for now.

My criteria for success was that the overheat trip didn't trip and it hasn't so far so that seems to be OK.

I can't totally answer your question as I haven't (yet) studied it closely. What seems to happen is that the worst time is first thing in the day when the house is cold and the boiler is firing for a long time to get everywhere warm. That's when I have seen/heard the pump running from my new thermostat. What then happens is that after a while the room stat calls for heat, which then opens the motorised valve and that obviously cools the boiler down much quicker until it fires again.

I wanted a stat that was in an enclosure, and also one that had a range over 110 so that it wouldn't suffer if the boiler got so hot that the overheat trip went. So I got this one from BES: Capillary Control Thermostat - https://www.bes.co.uk/capillary-control-thermostat-9781/ which has a range of 50 to 300C which is why I said the setting was about 90! This was the best one I could find - I expect you'll now point me to a much better one :)

Once I've studied how it's working I'll post here. I might also be asking you why my room stat appears to be short cycling the boiler - but not now...

Graham
 

SJB060685

Plumber
Messages
2,273
Looks a pretty good little control thermostat. You say the roomstat appears to be short cycling your boiler? I'd it only happening during a demand for heating?
 

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