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W-plan pump run on

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Discuss W-plan pump run on in the Boilers area at Plumbers Forums

davidwf said:
not sure why they have labelled it as normally closed.....it is closed whilst calling for heat, exactly as shown
Click to expand...
That is standard nomenclature. The contacts "normally closed" are connected when the thermostat is not doing anything, i.e. not hot.
When heat is applied, i.e. the system is activated to produce heat until the set point is reached, then the contacts will eventually open and the heating stops.
If you called them 'normally open', and you connected those contacts to the heating, nothing would happen!

Same with a relay. "Normally closed" means the unactivated state.
I was just brought up with this convention in electronics, and don't understand the issue!
 
surely "normally" equates to satisfied - i.e. the water HAS heated up and no further action is needed....so in its' normal state it is satisfied .....the connections and make / break indications are correct, just the nomenclature is confusing
in a roomstat the contacts are normally (i.e. satisfied) open, closing when heat is required
we could probably argue and counter argue this until the cows come home.....😁
 
the only other thing I can think of - but dont understand why - is that the 15mm bypass gate valve around the pump was open about 2 turns
As the system has no TRV's I have fully closed this now.....could it have possibly affected anything ?
I understand WHY it is provided on a system with TRV's but not in this installation........this is a W-plan system remember so surely as the diverter will be either HW or CH (or, if it ever gets stuck, somewhere in between as was the original issue) and with no TRV's fitted to any rads there is no need for a bypass valve / loop as the water will always have somewhere to circulate
 
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This is similar to your one, I think the description might be less confusing if it just left out the "Normally" and describe it like on the EPH pipe/cylinder stat.






1725967916241.png
 

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davidwf said:
the only other thing I can think of - but dont understand why - is that the 15mm bypass gate valve around the pump was open about 2 turns
As the system has no TRV's I have fully closed this now.....could it have possibly affected anything ?
I understand WHY it is provided on a system with TRV's but not in this installation........this is a W-plan system remember so surely as the diverter will be either HW or CH (or, if it ever gets stuck, somewhere in between as was the original issue) and with no TRV's fitted to any rads there is no need for a bypass valve / loop as the water will always have somewhere to circulate
Click to expand...

One could understand if the bypass was between the boiler flow and return because (on a Y plan anyway) a separate 2 port Motorized valve is supposed to be installed additionally on the cylinder coil because it fails shut whereas a MPV or Diverter valve will fail open to the cylinder.
 
Well I dont know........having previously tested and fully confirmed correct operation I was confident it would be OK.....which it seems it has been for a while but yesterday I got "the call"........and sure enough the rads are getting hot when the HW is running and the wallstat is off 🤬 ...I have also replaced the wall stat for good measure.
The motorised valve appears to be operating as it should - I haven't removed the cover but the indicator lever seems to be moving correctly but the CH pipe is definitely getting hot.
Wondering now if it's worth doing it properly and converting to fully pumped Y plan .......I THINK it will only need re-wiring (and of course a new 3 way valve) and I would fit a programmer at the same time ..
the only thing I can think of is that the valve is sticking or is not sealing due to debris but the original water was clean and I drained and refilled it adding Fernox anyway..
..
....any better suggestions ?
 
davidwf said:
Well I dont know........having previously tested and fully confirmed correct operation I was confident it would be OK.....which it seems it has been for a while but yesterday I got "the call"........and sure enough the rads are getting hot when the HW is running and the wallstat is off 🤬 ...I have also replaced the wall stat for good measure.
The motorised valve appears to be operating as it should - I haven't removed the cover but the indicator lever seems to be moving correctly but the CH pipe is definitely getting hot.
Wondering now if it's worth doing it properly and converting to fully pumped Y plan .......I THINK it will only need re-wiring (and of course a new 3 way valve) and I would fit a programmer at the same time ..
the only thing I can think of is that the valve is sticking or is not sealing due to debris but the original water was clean and I drained and refilled it adding Fernox anyway..
..
....any better suggestions ?
Click to expand...

On HW only, actuator unpowered, you should feel a fairly stiff resistance immediately on pulling on the manual lever, if you do and IF the actuator is attached to the valve spindle then the valve must be positioned correctly to port B (HW), so either the valve is passing or there is some form of reverse circulation, you could just remove the actuator and ensure the valve manually to port B only.
You say "the CH pipe is definitely getting hot.", I would expect the CH pipe to get hot due to conduction (if copper) for a maybe a foot or so but wouldn't expect even the rad tops to become hot.
You might try and see where the cyliner coil returns to the boiler and its position in relation to the rad returns.
 
IF I do decide to change it to Y plan are there any recommendations or avoids regarding makes.....would like to avoid the cost of the Honeywell one if possible but clearly don't want to be replacing it again next year because I bought a cheap one.
 
S plan it eph
 
Look up MOMO mid position valve, these apparently are only powered while changing position or modify a normal MPV, it will then allways return to the unpowerd state, only requires a extra relay.
 

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thanks.... that looks interesting rather than having the motor in a stalkled position 99% of the time.....they seem to be quite rare though
Can anybody recommend / avoid a "normal" spring return one ...
 
davidwf said:
thanks.... that looks interesting rather than having the motor in a stalkled position 99% of the time.....they seem to be quite rare though
Can anybody recommend / avoid a "normal" spring return one ...
Click to expand...
You can see if you read through the attached Link that the MOMO actuator contains far more circuitry than the conventional MPV, I definitely know that the modified MPV above, (I actually got that nice schematic from the attached Link), certainly seems to extend the MPV lifespan as a very old electrical friend of mine did this very mod years ago, he has since passed on but the MPV is still there and must be ~ 15 years old now. You have a electrical background? so should have no problem in implementing it. Some, mistakenly think that just programming on the HW last thing at night for a few minutes is enough to power down the MPV and it will, but only if the cylinder stat is also, very unlikely, calling, there should be at least a 6/7 hour powerd off state alone each night with the mod since CH is normally the last port of call at night.

Motorised Valves - DIYWiki

wiki.diyfaq.org.uk wiki.diyfaq.org.uk
 
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davidwf said:
thanks but......for simplicity I think I would prefer to go with a conventional 3 port spring return motorised one
Which to avoid though ????
Click to expand...

Honeywell, I believe, were the go to product at one time but maybe not so much now, I hear good reports of EPH though.
 
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We use eph stuff all the time very reliable but I still wouldn't fit a 3 port valve.
Your draining down and saving £30 against two 2 ports ain't worth doing .
Y plan = shorter lifespan and more difficult to trouble shoot.
 
OK, I get the idea (and potential benefit) of S plan and I would be quite capable of plumbing it myself....but....the boiler has an overrun that pumps for around 4 mins.....I already have a manual bypass valve (which is closed as there are NO TRV's in the system) but the bypas loop is literally a 15mm bypass around the pump so surely there will be insufficient "loss" in the simple pipework to dissipate the heat?
As it is, the overrun will pump around the HW circuit
and.... 2 x zone valves are considerably dearer than an EPH mid/3 position one which I can get for £65
 
You can get a (3 port) diverter valve that will give you CH or HW, you can also get a (3 port) mid position valve to give CH only, HW only, and CH&HW, thats why its called a mid position valve.
 
Convert from what?, a S plan which has separate 2 port valves for CH & HW or a W plan which has a 3 port Diverter valve as above but only gives CH or HW.
 
convert from the existing W plan...
If I changed it to S plan, when both are satisfied there would be nowhere for the residual heat to circulate ....as mentioned, the bypass loop appears to be just that - a 15mm pipe around the pump which I am not sure IS a bypass loop as such
"only" CH or HW is fine as it is quite a small house and the HW requirement is low
 
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