No heating without programmer set to hot water?

Hi all

I moved into a property approx 18 months ago and i've had a problem with the central heating where the radiators only get hot if the programmer is set to BOTH central heating and hot water. I've been ignoring it for ages while I got more pressing matters sorted but i've finally reached it on my list of jobs!

The boiler is a Baxi Solo 18HE

The programmer is a Siemens Landis & Staefa RWB2E which has two sliders, one for central heating and one for hot water.

There is a very old room thermostat (not sure of model but it's branded "Satchwell").

If the slider for hot water is "off" and central heating is "on" then the light on the programmer comes on, but nothing happens.

I had a read up on how the system should be working, and found a 2-port motorised valve and pump near the airing cupboard. I thought the problem might lie here.

With the programmer set to heating "on" and hot water "off", I adjusted the room thermostat to the minimum setting, and then checked the motorised valve and the override lever was providing resistance. I then turned the thermostat up to the maximum, and heard a noise from the motorised valve, the lever was now "loose" which I believe means the valve is now open.. but nothing happens at the boiler end... but I guess the motorised valve and thermostat are working ok?

Once I switch the programmer's hot water setting over to "on" the boiler fires up and the radiators start getting hot eventually, although it does seem to take rather a long time (not sure if thats actually a fault or just the performance of the system..). I've bled them and didn't really get much air out of any of the rads.

Any ideas how I can get the heating to work independently greatly appreciated... it should work that way, right?

If you have a 2 port valve, you need to check the heating one. My suspicion is you may have a 3 port valve, which when asking for heating maybe stuck or not making a microswitch contact inside. Can you upload a photo of cylinder cupboard?

edit
never seen that you had a motorised valve, if the valve is opening but boiler not firing them most likely a faulty microswitch in the zone valve

It may be a restriction of the plumbing. Some older systems can't allow the heating to be on unless the hot water is on too. However, you refer to a 2-port motorised valve, so this set up would be less likely. Having said that, most systems have a single 3-port valve (aka Y-Plan), or two 2-port valves (aka S-Plan) but you only mention the one 2-Port valve.

Assuming that there are two, 2-port valves there may be a fault with the heating motorised valve. The motorised valve is wired to the programmer room thermostat, and when heat is required by both they open the valve. Inside the motorised valve is a small switch that in turn starts the boiler & pump when the valve is fully open. My guess is that the controls are opening the valve OK, but the switch doesn't operate so the boiler doesn't start up. Then when the hot water valve opens, the switch inside that starts the boiler & pump so both the heating and hot water can work. If this was the case though, once the hot water cylinder heated up and switched off, the radiators would go off too. Do they?

Ideally we would need to know more about your system, if you have a Y-Plan / S-Plan / Pumped heating with gravity hot water circulation / something else.

Thanks for all your replies everyone, i'll get some more photos of the system up when im back home this evening. There is a water tank in the loft, but I can only find the a single motorized valve, if there was only one would this be how it's always supposed to work (heating only with hot water)? I guess it's just me being confused based on the programmer having two independent controls, i guess a single channel one should've been fitted.

I'm really a beginner to learning about heating systems so im not sure if I have S-Plan or Y-Plan etc .. I did a bit of reading up on it and S-Plan systems should have 2 valves, and Y-Plan a 3 port valve (mine is definitely 2 port)... but i'll get some pics and maybe make a drawing of it and hopefully that will help me totally understand the system.

I think though based on Stem's reply, it could actually be a limitation of the system. It's mostly very old and probably original to the property (early 80s), apart from the boiler, of course, I think there is a sticker on it somewhere with 2012 written on it... it's really annoying a combi was not fitted, as the airing cupboard wastes a lot of space and it's only a small property with a single bathroom. Unless it's hiding somewhere I can't find any other motorized valves, just the one.

post a pic of the valve that you have found and what it is connected to

The C plan changed through the years, the original had no motorised valves, and as time went on a tank thermostat and motorised valve was added, often as an after thought, and not always following a plan, S plan normally had two x two port valves, but my own central heating has motorised valve to stop central heating working but nothing on the domestic hot water because without the motorised valve in the summer it thermo syphons to up stairs rooms.

The early programmers were called 10/16 programs, and they had both a physical stop and an electric switch to set between the two modes, the way they counted 16 programs was a bit suspect 4 times 2 options both CH and DHW is how it was counted I would have counted that as 4.

It is not as bad as it first seems, as if the DHW is hot then thermo syphon is naturally reduced so it does not waste much energy really, at least in winter, the problem is in summer deciding how long to run the boiler for if there is not cylinder thermostat. This was designed to allow you to leave heating on, and it would only fire up when required, the idea was without the pump running the central heating would not work, however in both first house and this house it did.

First house around 1981 decided I had to do some thing so all three children could have their own rooms, so cylinder removed and airing cupboard made into a bed room and a Main 7 water heater fitted in integral garage, so two boilers one for central heating and one for domestic hot water, at that time the combi boiler if it existed was rare.

This house fitted motorised valves, 14 rooms so not short of space, and like the idea of being able to use electric, and in real terms oil combi boilers are just a boiler with an integral cylinder, as they can't modulate enough to really work direct. It seems your boiler was made in both modulating and non modulating, and it was designed to work with either wall thermostat or all TRV's. With wall thermostat it seems the P/F terminal was not used, but with all TRV it was used. However it would seem the instructions I am looking at came out in 2014, that does not line up with a 1980's system.

I am not sure when Part L building regulations came out, I think about 1991, I don't think the thermo syphon domestic hot water was allowed under Part L, so unless the same boiler has been made for 25 odd years, it seems unlikely the old system I have shown would be used.

It looks like I might have the "C plan" system that you describe ..

Here is a photo of my cylinder:

And there is a timer near it, i guess for an immersion heater?


On the other side of the wall, there is another cupboard in the bathroom, which contains the following pump and motorized valve:

Yes timer is for immersion heater, and looking at the cylinder I see no thermostat, so like mine it seems you can only adjust DWH by controlling the time it runs for.

As to valve not sure what it does, it seems both DHW and CH is pumped but only one has any valve on it.

If you look at a standard S Plan then the motorised valve works both as a valve and a relay, the orange wire from the valve powers the boiler and pump and also stops any back feed, but even if you fit a second motorised valve, the problem is getting the cables to the cylinder and adding a thermostat.

Years ago I fitted a wireless tank thermostat for my dad, but when I came to buy one, it seems they are no longer sold. I am sure there is a way, did find a Danfoss unit but £120 price tag seems a bit OTT.

You don't have a C Plan, because:
1) The feed to the hot water cylinder would not go via the pump
2) The motorised valve would be in the branch feeding the hot water cylinder
3) A C-Plan would allow you to have independent control of the heating and hot water

It's difficult to be 100% certain when only part of the system is visible, but from your photos it would appear to me that the arrangement you have is this:



In which case @ericmark is quite correct there isn't a motorised valve to restrict flow to the hot water cylinder, and the single motorised valve is there to stop the radiators heating up when just the hot water is required. To get independent control of the heating and hot water a second motorised valve would be required, this would create what is known as a 'S-Plan' as below....



...or alternatively replace the existing 2-Port valve with a 3-Port one as below. This would create a 'Y-Plan'



That's the easy bit. Unfortunately then the system would then need to be rewired from scratch as below. The wiring of the two systems are similar, but there are subtle differences.

Thanks for all the useful info, I guess I have a "no-plan" system

It looks like as suspected, its just a limitation of the current plumbing, from thinking further about it and looking at Stem's diagrams, the motorized valve just stops the radiators from heating up when the programmer doesn't ask for it, but i'd need a valve on the other "side" (or a 3-port valve) in order to prevent the hot water cylinder from heating up.

I think i'm going to just leave it as is for now as ideally next year I want to get rid of the cylinder entirely and have a combi boiler fitted. That will give me some extra space to install a walk in shower in the bathroom (in theory)..

If this doesn't go to plan, I will possibly revisit converting to S/Y plan system,

At least now I understand why the system works in the way that it does

Thanks all for your help.

Quick follow up to this one, in addition to my confusion of the original post I found that the RWB2E programmer was actually faulty and wasn't switching off reliably!

I have replaced it with a Drayton LP722 which has a jumper on the back for "Gravity Fed (G)" and "Fully Pumped (P)" modes. Once this was set to "G" mode the programmer will automatically turn on the hot water when the central heating is requested, avoiding the issue from the previous post (and much easier to explain to anyone who visits the house during the winter!!)

Still planning on sorting out a "proper" solution to this problem, its still really annoying having a cylinder heating up for no reason (I have an electric shower) but i'll handle that when I re-do the bathroom next year which will involve removing the cylinder and having a combi boiler fitted.