What type of central heating system is this?

[Simon Hawthorne]

Hi

I am in the process of fitting TRVs to all my rads (except the two in the rooms where the room stats live) - and wondered if you could help with a question about my current boiler. I thought it was a 'gravity' system.

I have put some photos of it here (when the server will let me upload them anyway!)

system is set up in such a way that I can eithe rhave hot water on, or heating and hot water - I can't just have heating. I have also noticed that when the room stats have reached the set temperature, and close the zone valves, the pump still works. Is this normal? Where is the water going?

There is also green marks on nearly all the soldered joints between pipes - is this normal?

I am in the process of designing a new CH system - but in reality, it is probably 6 months away yet - one that will cope with a loft conversion, and about 10Kw of extra rads (in a barn that is attached to the house) - so am not about to do anything drastic.

Thanks in advance

Simon

[IMM]

Simon,

It almost certainly has gravity hot water with an old cast iron boiler like that. At least it has zoning of upstairs and downstairs.

What are you future requirements? How many baths, showers, etc?

[Simon Hawthorne]

Thanks IMM

Should the pump always run then - even when the room stats have closed the zone valves?

Cheers

Si

[Lurch]

On Sat, 20 Nov 2004 17:00:57 +0000, Simon Hawthorne strung together this:

It is, on the water side anyway. Gravity sytems are generally pumped heating and gravity hot water.

Well, it's one way of doing it.

Don't know, can't see the piping that well in the pics, it's probably pumping against the closed valves, unless there is a bypass between the pump and valves. You should be able to spot this yourself, it'll be a pipe between the flow and return with a valve on it.

Yes.

Good idea!

[Lurch]

On Sat, 20 Nov 2004 17:13:56 -0000, "IMM" strung together this:

WTF are you banging on about? I've seen plenty of old cast iron boilers on Y plans. Don't know if you know, but it's the way the pipes and controls are connected to each other that determine the type of system, not the compound of metal used in the boiler manufacturing proccess.

[Set Square]

Basically, the pump is running because you're not telling it not to! The pump is not a positive displacement device, and will simply run "stalled" if the water can't go anywhere. You really need a room stat in each zone, in a room which *doesn't* have a TRV - and use this to close the respective zone valve, and turn the pump off when both valves are closed.

You do indeed have a gravity hot water and pumped heating system. The problem with this setup is that you can't have CH without HW because the boiler needs to be on for the CH and, whenever the boiler is on, you get gravity HW circulation.

In some cases, you can improve this by converting it to a C-Plan system - by putting a zone valve driven by a cylinder stat in the gravity circuit. See

provides a "boiler interlock" which turns the whole lot off when both HW and CH demands are satisfied.

Your system is a bit more complicated though, because you've got *two* CH zones. You could probably devise some sort of combination of a C-Plan and S-Plan system - but it would need a bit of thinking about.

It's probably a bit of corrosion caused by the flux used in the soldering process rather than indicative of a leak. Clean it up with wire wool, and only worry if it quickly re-appears.

[Simon Hawthorne]

Hi SS

I do have this - two zones, two room stats - and when both stats close the zones, the pump continues to run. There are no TRVs in the rooms with stats - and won't be.

Do you think it could just be a simple wiring fix?

Thanks

[Simon Hawthorne]

Ahhh.....I see...... makes sense.....

[Set Square]

Yes, but unless you also put a zone valve in the HW circuit, you can'e achieve a boiler interlock - so the boiler will continue to cycle on its own stat, and waste energy.

To fix the pump problem (i.e. simple fix without boiler interlock), it needs to be wired thus: The CH ON terminal on your programmer needs to be connected to the input side of both room stats. The output side of each stat needs to connect to the motor feed in its respective zone valve. The other side of the zone valve motors should be connected to neutral.

Each zone valve should have a pair of "volt-free" (i.e. not connected to the motor) contacts which close when the valve is in the open position. The COM terminal on these contacts on both valves needs to have a permanent live feed - or at any rate, a feed from CH ON on the programmer. The NO terminal of both sets of contacts needs to be connected to the pump's live terminal.

The pump will then only run when either or both valves are open - which will only happen when either or both room stats are calling for heat.

Hope this makes sense!

[logized]

It may be because your zone valves do not incorporate a switch contact to disconnect the pump when closed - you could probably tell by checking how many wire connections to the zone valve. Modern types have at least 5 connections (two for the valve motor, two for the contacts and one for earth). e.g.

typical wiring diagram is here -

[Ed Sirett]

My guess is the CH timer drives the pump and boiler. The wall thermostats drive the zone valves. The timer is probaby set so the HW heating is always implied with any heating ("10" or gravity mode).

Very likely the flow to the HW coil is also the vent pipe pipe. Likely with this type of installation the feed pipe (if it not combined with the vent ) goes to somewhere near the boiler returns from the HW coil.

With care it might be possible to make this system fully pumped using two pumps and an extra zone valve. It shouldn't matter if a pump is running in a stalled condition, but graeat care has to be taken to make sure that pumping over or sucking air won't happen.

[Keith G. Powell]

This operation appears to be the same as my 1980s bungalow CH which it is not a gravity system. It is fully pumped.

Below the thermostat set temperature, the 2- port valve is open, so water is pumped to both radiators and the DHW coil.

When the thermostat set temperature is reached, the 2-port valve is closed, so water is pumped to the DHW coil only.

That is the pump runs continuously. After the pump, the pipe Tees off to the

2-port valve and to the DHW coil(via a stop c*ck).

The DHW cylinder does not have a thermostat.

The timer also allows either DHW or DHW with CH or both off.

Hope that makes sense

Keith G. Powell

[Lurch]

On Sat, 20 Nov 2004 23:42:14 +0000 (UTC), "Keith G. Powell" strung together this:

That's not fully pumped, that's some lame attempt at plumbing. It's a cobbled together hybrid system and should be discounted from any country wide energy efficiency and heating type surveys.

[Keith G. Powell]

Why is "my" system not fully pumped? Both the CH and DHW circuits are pumped. No gravity/convection circuits involved.

I illustrated "my" system to show one reason why a pump would be running continuously - not to advocate it. I make no claims about efficiency. But if a survey was held about efficiency of installed systems, and it was ignored, it would be a misleading survey. Besides, all systems are not 100% energy efficient.

Yes, it could be more efficient - just by adding a DHW cylinder thermostsat and a bypass and a bit more wiring, etc, etc. But that was not my point.

Keith G. Powell

[Set Square]

No according to the OP's description! He said that the pipes to the right of the boiler - which are *not* in a pumped circuit - go to the heating coil in the cylinder, and that the two zone valves are for two different heating zones. He also said that he can't have CH without HW. All this is consistent with a gravity HW system.

Of course, he *could* have got it wrong. The pipes on the right *could* just go to the F&E tank, and the zone valves *could* be one for CH and one for HW. But that is *not* how he described it.

[Simon Hawthorne]

The pipes on the right run straight to the cylinder. I also have two CH zones (upstairs & down) - the valves are for each circuit....

Thanks SS for yout time in describing how, with some wiring, I could stop the pump running. If I'm honest, I think it is beyond me........! Think I'll wait until the summer - when I change to boiler..

Many thanks

Simon

[Ed Sirett]

Your system is fully pumped. What you don't have (like a great number of older systems) is independant control of the heating and HW.

The system the OP showed us and described is a pumped 2 zone heating system with gravity indirect HW.

There are scopes for energy savings to be made on these systems. Whether or not this is worth doing will depend on many factors.

A large one will be how many years of life the existing boiler has left in it. If it's up for replacment in the next few years it may well not be worth trying to make improvements just yet.

[Keith G. Powell]

[IMM]

Does it?

[Keith G. Powell]

Agreed :o)

Thought I'd just give my example of continuous pump and where water was going, just in case OP's sytem interpretation had got it wrong.

Keith G. Powell