I plan to install a new twin-coil solar HW cylinder soon, and plan to convert the CH system from gravity-fed to fully pumped at the same time. (Solar coil to be utilized at a later date) Currently the boiler and pump are downstairs with 28mm gravity-feed pipes and 22mm CH pipes heading upstairs. There is currently 1 thermostat downstairs, and no cylinder stat. TRV's on all rads but 1.
I plan to utilise the original pipework where possible but move the CH pump to upstairs and install a motorized valve to divert flow between CH and HW. I'll also fit a cylinder stat.
I *could* also use a motorized valve to create upstairs & downstairs zones if worthwhile. The programmer supports fully pumped with cylinder stat and (I think) 2 zones - will check.
Any recomendations from the group of which CH plan to go with and whether it's worth creating upstairs & downstairs zones?
Any suggestions on plumbing config and type of motorized valves to use?
A lot depends on the layout of the existing pipework. Presumably there are 4 connections to the boiler at present - 2 for the HW and 2 for the CH? If you go fully pumped with a single pump, you'll only need 2 - although you could keep separate returns, and have 3, if that was easier.
How is the downstairs CH circulated? Is it below the downstairs floor so that the CH pipes going upstairs are only for the upstairs rads, or does it
*all* go up and then come down to each individual downstairs rad?
If you have a single pump upstairs, *everything* (including the water for the downstairs rads) has to go up, and then be distributed using zone valves - probably in the airing cupboard. The ease with which this can be achieved depends on the current setup.
If it is difficult to achieve this, an alternative fully pumped strategy is to keep the existing pipes and simply insert a second pump into the HW circuit. You would control the pumps with the respective room and cylinder stats, and you then need a bit of relay logic to turn the boiler on whenever either pump is running. You would also probably need an anti-gravity valve in the HW circuit to prevent any flow when the HW pump isn't on.
Assuming that a single pump solution *is* viable, an S-Plan+ system would give you the most flexibility - and allows you to have as many zones as you wish. Whether or not it's worthwhile having separate up and down zones really depends on how you use the rooms. If there are long periods when you only want to heat upstairs but not downstairs, and vice versa, then it is a good idea. However, you need to consider whether the bathroom needs to be warm all the time. Going back to the question how about the CH is distributed, if you have a single 'between the floors' circuit it will be very difficult to have up and down zones. On the other hand, if they're already separate, you'll have to solve the problem of getting the downstairs radiator water upstairs and back down again.
If you *do* go for zoning, I would recommend using a programmable thermostat for each heating zone. It doesn't then matter whether the main programmer supports zoning - you just leave the CH control on that set to 'on', and use the programmer to time just the HW.
For an S-Plan plus system, you'll need one 2-port valve per zone - so that's one for the HW and probably two for the CH. They need to have auxilliary 'volt-free' contacts which can be used to switch on the boiler and pump whenever one or more of the valves are open - as per the standard S-Plan arrangement. [See
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Any reputable make of valve - Danfoss, Drayton, Honeywell, etc. - should be ok. Even if you use the existing 28mm flow and return pipes from the boiler to the airing cupboard, I assume that you will use 22mm after the pump - so the valves only need to be 22mm.
On Mon, 26 Mar 2007 11:42:11 GMT someone who may be "Alan" wrote this:-
It is often simpler to add a pump to the former gravity circuit and leave the central heating pump where it was. These pumps can then be controlled by a thermostat and time clock as appropriate.
The only major thing to watch is that the gravity circuit was often used as an expansion pipe and this must not be interfered with.
Depending on the arrangement of the building it can be better to have north/south zones rather than top/bottom. However, this very much depends on how rooms are arranged in the house.
Thanks for the informative response. There are 3 pipes into the boiler - the return from the gravity circuit goes in via a "Y" piece with the CH return. I will need to cap off the current gravity output from the boiler and just use the remaining 2 connections.
The output of the pump is teed and one leg feeds the downstairs CH circuit and the other goes upstairs on one of the 22mm pipes. Adding a 2nd pump isn't an option I had previously thought of, however from what you say I can achieve what I need to with 2 or 3 valves. The pipework for downstairs is all below floorboard level and starts and ends by the boiler, so converting to seperate zones would be reasonably easy, but as every room is used daily there may not be much point.
I will look at the S-Plan+ details, sounds like it's what I need.
Ok, this needs a bit more thought! Is the pump in the flow or the return?
For a zoned system, the pump needs to be in the flow pipe, and needs to be
*before* any zone valves. You're going to have to leave it where it is rather than moving it upstairs - otherwise the downstairs heating circuit will tee in in the wrong place.
You could put one valve in that circuit, just after the tee, and two more valves upstairs. At the top of the upstairs heating feed, split it into two - with a valve in each leg - connecting one leg to the existing upstairs heating circuit and the other to the coil in the HW cylinder.
With regards to the existing HW gravity feed, leave that comnnected to the boiler as a vent pipe (the top probably already goes up and over the F&E tank?) but blank off the connection to the cylinder, using the pumped feed instead.
Ahh, OK, so three paths for pump output, depending which valve(s) are open.
Yes, one gravity pipe goes to the F&E vent, the other is the tank's output into the CH system (to fill it etc). Both currently have unequal (28x18x15) tees at the cylinder connections. I could replace the tees or blank off the existing cylinder connections and use the new valve output instead then.
So 3 valves, a cylinder thermostat, and maybe 2x programmable room thermostats is probably what I'll need then.
Yes. You'll still need a valve on the downstairs circuit even if you parallel it with the upstairs one and use a single room stat for the whole house - otherwise you won't be able to have HW without downstairs heating.
Agreed - looking at various bits on screwfix's site now. The programmer Honeywell recommend is the ST6400C - which is the one I already have. The existing room thermostat is a digital one. I could re-use this and just add another room stat upstairs? (This option would give independant HW/CH operation controlled by the programmer and upstairs/downstairs temperature control (when CH is on) via each stat)).
Many thanks for your help. Guess what I'm doing over easter.....
Make sure you know the score if you consider pumped return arrangement. I inherited a system with pumped return and could not get it to perform. With pump speed sufficient to heat the house in a reasonable time, there was a serious issue with pump over into the header tank. If you are intending to stick with a vented system rather than going sealed, would recommend you opt for pump in the flow with make up water connection close to vent.
Last autumn I converted my house. It is 2 storeys and has a solid ground floor. The C/H distribution is between the two floors. Installing separate distribution for each floor would have been very difficult, so I just have one zone. The system is controlled by the same programmable thermostat (Danfoss TP9). The sensor is in the sitting room. I find that I can achieve a sensible heat distribution throught the house by a one time setting of the radiator valves.
My pump is on the return just before the boiler where it always was. The new valves are just before that.
The expansion is unimpeeded via the old gravity H/W flow pipe.
I installed a new feed from the header tank which connects between the pump and boiler - so there should always be water in the boiler.
(The original feed was via the old gravity H/W return pipe. )
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