pump overrun

...Lastly, and grabbing at straws here, if the bypass valve was almost fully closed and the bypass loop really (really) small, I guess the strain on the pump could cause it to heat up and thus heat the water in the loop...
Not a chance
1. As long as the pump is wet, it will not get significantly hotter due to strain.
2. Even if it did, pump is only 0.1 A, not enough to heat up pipes + boiler.
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Hi guys and thank you very much for contributing to my thread. The bypass loop is about 5 m. long and runs in 22mm. When there is no call for ch nor hw, I observe the port valves swing back to shut off position and the boiler shut off and stay shut for the time there is no call. During pump overrun, the flow and return pipes to the hw cylinder go lukewarm. I checked the bypass gate valve and was more on the shut side. I have opened it a bit more ( more like in the middle) and I ll see what happens....hopefully the hw and ch heating time won't take much longer! I ll keep you posted tomorrow morning. Once again I really appreciate the time you have been putting on this issue.
Bengasman raises a fair point. The older 15/50 pumps did draw 150w at full speed but it would have to be a very small bypass loop and boiler for this much energy to heat it significantly.

It's really simple, hot flow pipe = boiler on.
The real question is: why does it come on and when?
Logical options:
Dodgy valve switch
Dodgy timer
frost stat
that sort of thing
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hi bengasman.............i think i owe you an apology!!You were dead wright in assuming that there should be a source of heat coming from somewhere to heat up the bypass. Yesterday evening when i came back from work and posted you guys, i spent 2 hours checking the system and indeed, as you, in one of your first answers to my thread mentioned, the boiler does come on even if there is no call for ch or hw!!!! :confused: I even switched the programmer from TWICE ( that's where i normally leave it) to OFF for both ch and hw and even though the boiler switched off straight away, it switched back on after 2 minutes :confused: even though the programmer was on position OFF. The boiler carried on the ON and OFF cycles for ever and also the pump kept spinning. In order to stop the boiler firing i turned the boiler stat knob to ZERO and that stopped it. However the pump kept spinning forever and the only way to stop it was to switch the external electricity switch to the programmer to OFF.The motorized valves do not swing into open position when there is no call for heat despite the boiler keeps firing. Also, no heat is going through the valves when there is no call. The heat only goes through the bypass loop . So that tells us that the valves are closing and opening properly. So as you mentioned early on, the micro switch of one of the valves must be sticking. That statement leads to a few questions:
1) To find out which valves is the culprit, would i do the wright thing if i disconnected the motorized valves cables, one at a time, from the junction box so to see which one keeps the boiler firing? Or there is another way?
2) Once i find out the faulty valve, do i replace the motor only or the whole valve would need replacing?
The motorized valves brand name is ACL Lifestyle 22mm. 679h308-30L1. Are they widely available?
If they are not widely available, can i replace it with a Honeywell one and would the wiring be the same? Just in case you need to know it, the programmer is also a ACL Lifestyle and the junction box is Honeywell.
4) If i need to drain down the system, how can i open these motorized valves manually? I know that with Honeywell ones is straightforward, but i tried to do it with the above mentioned valves and i could not do it. They are very hard and i do not want to force it just in case i break it.Any tips on that?
5) Lastly, ( that is if i need to),any tips on how i can remove the valves? There does not seem to be much movement when i try to move the pipes
Once again thanks a million for being so patient.
turn off power to heating system test power is off then as long as your system is wired up correct just locate 2 grey wires from valves in thwe wiring box.
take one grey wire out,disconnect wire safe so it does not touch anything power up and see what happens,if fault cleared its that valve if not its the other.
best off changing both valves to be honest as tother will also go wrong in time.
yes its a drain down to below the level you are working,if pipes are crammed in close just discon pump,bypass valve nuts etc.
beware some cylinder tappings can leak afterwards so dont put to much force on these.
had honeywell valves fitted in a property buy they were noisey when closeing when boiler at bypass,kind of a shudder through pipes.
so fit draytons,cheaper.same colour wires.
Hi Johnnojob and thanks for replying. Today funny enough that problem has not reoccurred.When such microswitches stick, do they stick all the time or can they also stick on and off? Thank you
well thats the way to diagnoise which valve is faulty assuming all is wired up correctly already.
its not an immediate repair as its not causing any distress in this weather.
if fault returns and is a nuisance just turn down boiler temperature control to 0 when boiler should be off.
as your system is working leave the repair until you are prepared for a cold house.
can be intermittent.
Thank you very much for your help Johnnojob and also a big thank you to everyone who contributed very patiently to my issue. This is really a great forum with great people:)
It is quite common to find a sticking microswitch in two and three port valve actuators.

This can have the effect of the valve itself being closed (thus restricting water flow) but the live feed to the boiler is maintained (via the faulty microswitch) and this keeps both the boiler firing (from time to time) and the pump running, even if the controls are not asking for heat.

Many motorised valves can be repaired if you take the thing out yourself - if you are competent to do so. Google the SeeRed pages on Sunvic motorised valve failures to see more details.

Sticking microswitches in Sunvic 2301 two port valve actuators (for example) have produced just these symptoms for quite a few householders recently.

Sometimes the valve actuators can be mended with a new switch, sometimes the microswitch gets so hot it overheats part of the actuator base plate then the actuator itself is usually scrap.

The overheating of the switch occurs because the degraded internal switch contacts sort of weld together (but not very well) and pass current - albeit through a resistance. Current through a resistance = heat, so the switch heats up and sometimes even fries the baseplate of the actuator.

I'm loading some more pictures of failed microswitches shortly!
Unless you know these things inside out, I would advise to replace the whole head rather than try and fix it; it's not worth the agro.
No need to apologise for not knowing something that is not your field of expertise. When you know something inside out, it is pretty easy to put your finger on the root cause of the problem, even though it may seem like black magic to you.
Most of us will probably be as baffled about what you do as you are about all this.
The only actuators that are a DIY proposition to fix (and only then if you are well versed in hobby electronics) are the modern Sunvic designs.

But given that even these can have microswitch problems (occasionally) it's best to send the complete actuator for repair.

Many people have replaced capacitors in Sunvic actuators successfully and I continue to supply these parts upon request.

However, sending the actuator for repair means it should be tested on a test rig before being returned and any other problems fixed at the same time.

DIY is fine - so long as you know when to stop! This is the whole point of Internet guidance - there are many highly competent householders who just need a nudge in the right direction.

There are many others who are a menace even using a gas cooker, let alone driving a car - but for some reason they are still allowed on the roads.
Hi SeeRed and thanks a lot for your very professional input. I ll google it. Thanks again.

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