Discussion in 'Plumbing and Central Heating' started by Kellymont, 18 Sep 2011.
[/quote]Could i fit an electriclly operated shutoff valve in place of the bypass?
Could i fit an electriclly operated shutoff valve in place of the bypass?
because a proper bypass valve is designed to allow a set amount of water through depending on system load, for example when TRV's shut down, the bypass will open and let a bit of water through the bypass to relieve pressure. Your proprosing to allow all the water through the bypass circuit if the zone valves are closed, and have the bypass completely closed when the zone valves are open - if your doing that you may as well get rid of the bypass as it will serve absolutely no purpose what so ever. If you think about it, if the zone valves are closed then the boiler and pump will not be on, and it wouldnt matter if the valve was open or closed...and so to re-iterate, what your proposing makes no sense at all.
But the reason i am proposing a bypass shutoff valve is to let the hot water flow around the bypass loop during `pump overrun` only.
The rooms don`t get hot enough for the TRV`s to operate now yet alone when the weather does get cold and the room stat in the living room is constantley calling for heat, also the hot water takes ages to get to temperature so there should be no change in the load, and it is a vented system.
I am assuming that the hot water is short circuiting around the loop (as the pipe feels hot via the bypass valve) is causing the boiler to shut down
but i could be wrong?? Regards
so replace the bypass valve with a new unit rather than doing unnecessary modding. the bypass shouldnt let water through it all the time, but bear in mind that thermal transfer will heat the pipes around the bypass even if no water is flowing through it
The purpose of a pump overrun circuit is to dissipate residual heat from the boiler. Just sending it back to the boiler through a bypass completely defeats that object, and if it is a fixed bypass, it will raise the return temperature, which you do not want on a condensing boiler. All of this is a good reason for changing to a Y Plan and ditching the S Plan: you don't need a bypass and you won't raise the return temp.
The Vitodens 100-W Compact Heat Only Open Vent boiler has a return temp sensor. This will in some circumstances modulate the burner on a low-ish flow temp if the return temp is high. You can set the radiator knob on the boiler right around to the word 'reset', ie fully clockwise, to get the best flow temp. If the system is completely vented, there may, under some circumstances, be excessive flow through the boiler. You may need to reduce the pump speed to increase the temp rise through the boiler to about 15deg at full output. Adding weather compensation will do all of this automatically and improve economy.
The other snag with an S Plan is that frost protection won't work unless the pump runs and satisfies the internal flowswitch.
The only way you can use a plug-in timer on a Compact is with weather comp. The external demands are fed in via two low voltage [not 24v] connections, the DHW demand by means of a relay box with the appropriate weather comp kit specific to the Compact.
That's a good answer to a silly question.
Instead of messing around with unnecessary relays you could have thrown away the Viessmann timer and bought a boggo external one.
Most of us here would know how to fit relays but would also be intelligent enough not to bother. If I tried such bodges with customer installs they would be horrified.
I could have thrown away the viessmann timer, fitted the original back or a `boggo`one on the wall and lernt nothing.
This was a very tidy mod using quality parts that will no doubt last longer than a `boggo`one and my plumber commented it all looks very trick and tidy not a wire or any of his pipework in sight.
I would not expect anyone fitting for a living to go to this trouble but this installation is for my own consumption and satisfaction, Viessmann do Not make it clear that you also have to have weather comp for the timer to work with this model, they just say it is an accessary, i made it work and it has been fine for two months.
Fitting a `Y` plan is all good and well exept it has already been stated quote:- that i have a 26kW boiler a 3 port is a bit restrictive, you would need to bush up to a 28mm version and even then it would be borderline.
From recollection (I'm sure someone can Google it) Honeywell suggest around 86,000BTu is the max they recommend through a 3 port. For this reason we do not specify them for boilers over 18kw.
I got the plumber to fit a bypass valve and loop as i wrongly assumed it was a path to pump the hot water during boiler pump overrun when both zone valves were closed, if the loop was long enough the return water temperature would be lower, thus not stressing the boiler.
Question :- Can someone please explain to me where the hot water in the boiler is supposed to be pumped to during boiler pump overrun with a `S` plan system, or maybe it does not require it on this model, but the pump does run-on for some time when connected to the boiler.
Thanks Everyone, it`s a great little boiler and i ain`t lost the faith!
during pump over run the heat is supposed to be dissipated through some medium whether it be pipework, a none TRV radiator/towel rail or HW cylinder. This subject is widely debated and alot of people consider pump over run to be a waste of heat energy due to mass production boilers not being able to cope with latent heat in the heat exchanger and boiler casing. Whatever the heat energy is dissipated through, it IS a waste of energy, but a necessary evil on most modern boilers, as its better to lose the energy than to risk damaging components.
WB1B is one of the few boilers available where fitting a pump overrun is optional, if you weren't already aware.
there we go then, finally a decent boiler which is manufactured to fine tolerances and uses quality components to prevent the need for a wasteful over-run!
There are others, one of which is a condenser and has been in continuous production since 1982.......
I believe Poxi Batterton now make a heat only that needs no pump overrun too? Not sure about the model details because we don't install their stuff.
Thanks, but i`ll stick with the Viessmann, not looking for another boiler just yet, i know i have had two full months from it and the rumour is condensers don`t last long, and i`ll be well pushed to get it to last as long as the old oil Worcester (21 years) that it replaced but if i am kind to it and get the pump overrun to pump the latent heat somewhere sensable it stands a better chance of being reliable?
Honeywell quote up to 26kw for their V4073A/V4044C 22mm divertor valves.
Danfoss are less restrictive afaik.
I think the best wey out for me is to get the existing bypass to go via a longer rute then back to the boiler so that the ruturn water is less hot, the hot water that i believe is shorting back to the boiler causing it to shut down.
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