CH control upgrade: valve & circulation direction problem.

[CliveM]

Whilst it was warm I decided to add some controls (i.e none before) to the central heating system.

Exiting system is gravity (pumped heating). Two 28mm pipes out of the boiler, then a 22mm pumped circuit is taken of the 28mm pipes.

To keep things simple I went with what I think is called "honeywell C Plan". Wiring OK (after a google of this group) but I have a problem.

Before starting I put heating ok HW only, and checked which was flow & return. I then fitted the valve on the return pipe (with the correct flow direction A->B) was recommended doing a search and as access was easier.

After refilling I put HW and CH on, and then noticed that the water was trying to flow through the valve (i.e B->A) and that the pump was therefore in the return. (i.e when the pump was on, circulation was in the opposite direction to what gravity was running before fitting the valve)

With the HW & CH on the house got warm and all the flow/return pipes by the boiler but the HW coil did not heat. Putting the system to HW only also did not work. I suspected an airlock somewhere and tried to clear without sucess.

In the end I guessed that I must have been mistaken which pipe was flow & return and though that I have fitted the valve in the flow. I then drained the system again, and swapped the valve around so that the valve was in the flow with direction (A->B). Upon refilling the system, we now had HW/HW&CH/CH. When HW only was on, the only the HW feed got hot, then the HW return. CH was cold. All seemed ok.

This morning, put HW only on, and I notice that the water is now flowing in the original direction (i.e through the reversed valve B->A) and then up the HW feed. There is also now some gravity circulation up the CH feed (but no heat in any rad). HW is heating.

How can the water travel in opposite directions between gravity & pumped. Is it possible that gravity flow runs either direction for some reason?

Most importantly, which way should the valve be fitted, and how can I solve this problem?

[Set Square]

It sounds like it's the *pump* that you need to turn round, rather than the valve!

You say that you have ony 2 pipes going to the boiler - 28mm - and that the

22mm heating circuit branches off these.

In HW-only mode, gravity flow will be from the top of the boiler and return into the bottom. When you turn the pump on, the direction of flow through the pump will determine which way the water goes round the CH circuit - all the way back to the boiler - including through the bits of 28mm pipe which are shared with the HW circuit. Here lies the rub! If your CH flow uses the

*bottom* connection for flow (which isn't a good idea anyway, because the boiler thermostat will be at the top!) and the *top* connection for the return, this will interfere with the gravity flow - and either stop it altogether or make it go round the "wrong" way.

So make sure the pump is the right way round. Was your system ok before you fitted the valve? Have you touched the pump during your upgrade operation?

Incidentally, I doubt whether the valve really *cares* which way the water goes through it - but you might as well line up the flow with the arrow while you're at it. [Unless anyone knows different?]

[CliveM]

Been thinking about this untill I got a reply, and came to the conclusion that the pump should be reversed to that all the water goes in the same direction. Was a bit worried about reversing the pumped from in case it affected any of the TRV.

Yep, thats right.

Think you are right. When the HW is on (i.e gravity) water heats ok. When CH is on heating is OK. When HW and CH are together we get no hotwater.

System worked ok before, either HW only or HW & CH. Pump not touched only the valve put in place which seems to have affected flow.

[Set Square]

Seems very odd. Maybe the HW circuit has *always* flowed the other way when the pump is on, and maybe it doesn't matter.

Have you wired the valve *exactly* as per the C-Plan diagram in

?

The only effect of the valve (provided it is open!) should be to put a little bit of extra restriction into the HW circuit - but not enough to matter. [It *is* a 28mm valve, isn't it?] Have you checked that, when you are not getting hot water, the valve is actually *open* and that the boiler is still running for the CH? I'm trying to think of how you could have mis-wired it to make the valve close when the CH is on, but I can't instantly see how to do this. Anyway, it worth double-checking the wiring - and maybe getting someone else to check it too.

[CliveM]

Spent more time trying to work out what is happening, then fitting the control in the first place! - never mind good excercise up the ladder.

Yep, definatly a 28mm fitting - the bore through the valve is a bit smaller but shouldnt be a problem as the system gives HW only which is just gravity fed.

Wiring OK. If HW only, the valve opens, boiler fires, pump off. If CH only, valve closed boiler fires, pump runs, if HW&CH then Pump runs, valve open boiler fires. - If the valve is open and boiler on there should be HW.

I think you may have got its- its always flowed the other way round and no one noticed, even though it is a bit odd. The gravity circuit runs the oposite way round depending if pump is on or gravity only.

From what I can make out (and I think I understand it now) through the maze of plumbing, what happens is a follows.

When the pump is running, the CH return pumps from its 22mm into a T to the

28mm which then goes (Boiler Return ^ HW). This is resulting in 1/2 the CH return being pumped to the boiler, and 1/2 to the HW (which then becomes the Flow). When the HW pipes return it arrives at the 28mm T with the 22mm CH Flow comming off. As the HW return cant move the against the pumped CH flow, what happens is that the HW return water get "sucked off" the T piece by the pump (i.e CH FLOW ^ HW RETURN) so CH flow is a combination of Boiler Flow and the HW return. (or to make it simple, CH returned water is pumped as HW flow, and HW return if then pump round the CH circuit as CH flow)

This then results in HW being passed through the cylinder from the bottom up but is obviously pumped when pump is on.

And you wonder why I am confused about all this. Anyway this now seems to have resulted in that we do get HW when CH on (and it must have always been like this), but that I have just been confused over the last 3 days! I suspect that there was a load of air in the system which caused the initial problem. (you could hear it in the pump, and boiler cut out a couple of times), which now seems to have cleared.

Time to put the tools away (I hope) - thanks for all your help.

[Set Square]

Are you saying that it's now working ok?

Its not a very good idea sending "spent" CH water round the HW circuit, because it will already have cooled a bit, so HW recovery will be slow. At the point where the return flow from the CH rejoins (what is supposed to be) the return flow from the HW, it might be an idea to use a sweep tee rather than an ordinary one. If fitted with the sweep in the right direction it would be far harder for the water to go the wrong way.

How near the boiler is the point where the circuits split? Does your boiler have 4 connection points, two of which are currently blanked off? If so, and if the split is fairly near the boiler, you could consider having two totally independent circuits all the way back to the boiler with no shared pipework. That should definitely fix the problem.

Alternatively, you could convert to a fully pumped S-Plan system. You would need an additional, zone valve, and you would have to move the pump into the shared bit of pipework.

[CliveM]

Yes.

No boiler has 2 connections.

As it is working now (i.e there is hot water) - I will leave it as is for a week or too - and then replumb the system.