Can I use a Cylinder Stat on Pumped/Gravity Profile?

[JohnD]

my relation has a Profile 100E.

CH is pumped and DHW is gravity.

When the timeswitch is set to HW only, the boiler fires from time to time, when it gets cool enough to trip the boiler stat. This happens even if the cylinder is hot. The primary pipes to the cylinder are about 10m long, mostly horizontal. They were formerly uninsulated, but I have now sleeved with Climaflex where there is room, and wrapped in loft quilt where they are packed too tight. They run between first floor joists.

I had a look at the programmer fitting instructions (I did not note the make/model) and, on gravity DHW, it does not have an option of a cylinder stat. But I would have thought it would be possible

is there a way?

 

[seco services]

convert it to a c plan

 

[JohnD]

Is that fully pumped with a 3-way valve?

more work for me

Biggish house, so both CH and DHW are on 28mm pipes

Edited: No, the Wiki says "system where the hot water feed and the heating are pumped if it uses two zone valves it is usually refered to as S plan if i uses a diverter valve Y plan (see also motorised valve)" so what's a C plan?

 

[seco services]

gravity hw pumped heating.

should have a pic on honeywell site. http://content.honeywell.com/uk/homes/systems.htm

 

[JohnD]

I see

When Cyl stat is satisfied, it looks like it closes the 28mm valve, but does it also stop the boiler firing? It is a big iron boiler so takes a fair amount of heat to warm it up.

Thanks!

 

[seco services]

when the stat is satisfied valve shuts boiler shuts down

 

[JohnD]

you mean it will stop the boiler firing, if connected as shown? that would be great I have been burrowing under the floor (cough, cough) to lay a 3+E cable to the cylinder.

 

[seco services]

yes stop it firing unless heating is called for should be a wiring diagram as well on the site.

 

[JohnD]

yes there is, but it just shows which wire to which terminal, doesn't show what they do.

must it be the same Honeywell controller as shown, or are connections standardised?

 

[DP]

Indeed fitting a two port valve on the HW zone is sensible and gives you full control of HW temperature, but you can just by using a cylinderstat achieve the same result when only HW is selected. Boiler will still cycle on/ off due to the fact that the circulation is slow for gravity zone.

Converting to fully pumped is the way to do it. If you can spilt the sleeping from living areas, three zones are fuel saved and money in pocket.

 

[JohnD]

I really want to stop the boiler cycling when the cylinder stat is satisfied. Are you saying that C-plan won't do that?

 

[oilman]

Changing to fully pumped can cause grief io some systems. Just add valve. The connections are more or less standard.

The grey wire is the supply to be switched to the boiler. When the cylinder stat wants heat, the brown supplies the motor on the valve which connects orange to grey and runs the boiler. If the CH is wanted, the pump is connected too. If the water is hot enough, the brown to the motor is switched off, so valve closes and sets the boiler to connect via white, so boiler and pump run when heating is required.

And it does stop cycling.

 

[seco services]

no what hes saying is fitting a zone valve (c plan) is the way to do it.
but you can just by fitting a cylinder stat get the same result.
but converting it to fully pumped is better than the top two options and even better is to zone the sleeping areas from living areas

 

[JohnD]

It might not be the best solution, but if I can connect a cylinder stat and stop the boiler cycling when the cylinder is up to temp, that will reduce energy waste. It will also save me doing any plumbing and will be relatively easy and quick.

Can I follow the wiring diag on other programmers or must it be the one listed on the Honeywell diagram? A Drayton is currently fitted, possibly a LP111 (it does not have the curves on the face) but I can buy a Honeywell if I have to.

From memory the old one looks like this (but is not a BG version)

with set, test, + , -, yes, no buttons under the lower flap.

 

[D_Hailsham]

yes there is, but it just shows which wire to which terminal, doesn't show what they do.

must it be the same Honeywell controller as shown, or are connections standardised?

You need a two channel controller which allows you to set separate HW and CH times.

Here is how it works:

CH: CH on - T4 - CH Stat 1 - CH Stat 3 (call) - 5 - link to 9 (pump runs) - white to valve switch - orange to 10 (boiler runs)

HW: HW on - 6 - HW Stat 1 - HW Stat C - 8 - brown to valve motor (valve opens and switch moves over). Grey connects to orange and boiler runs.

The important thing to note is that the pump only runs if CH is being heated up.

If you just fit a HW stat you will be able to turn the boiler off when the HW is up to temperature, but you will not be able to stop water circulating through the pipes from boiler to HW cylinder while the CH is on. So the HW will continue to get hotter. The valve stops this unwanted circulation.