Can I use HW with CH drained down?

[Lobster]

I want to do some re-routing and radiator installation of my central heating here, which I'm likely to want to stretch over a couple of weekends (at least, knowing me!). If I do so, which will involve draining down the CH, will that still allow the boiler to heat up water as normal?

We have a gas system boiler, unvented HW cylinder, with HW and CH controlled separately via a timeclock (CH being switched off permanently during the summer).

Alternative would be to resort to the immersion heater, but I'd need to re- plan for minimal boiler downtime if that was needed.

Thanks

[Andrew May]

In a word No. The hot water cylinder is on the same circuit as the radiators and is switched by the two way valve so that the water from the boiler is used to hear the radiators and/or the tank.

If you drain down the CH system there will be no hot water to go through the heating coil of the tank.

So immersion heater it is, I'm afraid unless, perhaps you want to replumb the bit around the valve first - which itself would require the system to be drained down first.

Andrew

[John Rumm]

Chances are your primary CH circuit is also used to heat the unvented cylinder. There will probably be either a three port valve or a pair of two port valves somewhere to direct the flow from the boiler through the relevant bits of the circuit.

So in short, with the CH drained, there is no primary circuit, and you can't heat the water that way.

Immersion for a couple of weeks is probably going to be the best way. Also you can often structure the work so that you hang new rads etc and pipe them up before you make the final connection to the heating system (old rads can be removed, but both taps turned off to keep the system "live") thus keeping the total time drained down to a minimum.

[Dave Liquorice]

May not need to drain down.

Work out where you need to cut the pipe work, one in the flow and the other in return. Try an choose a place with access for a pipe cutter and enough movement in the cut pipes to enable the cut ends to be misaligned by about 2 diameters. Get four push-fit stop ends of suitable size. Useful to make sure they are releaseable. Find the expansion tank in the loft. Securely block the feed pipe in the tank and the expansion pipe overhanging the tank. You can get large rubber bungs to do this. Put a collector of some sort on old towels under where you are going to cut. Have the stop ends ready. Cut *ONE* pipe only. There will be some spillage. Quickly fit the stop ends to the cut ends. Repeat for other pipe.

Not quite clear on what you are intending, it sounds a bit more than just moving a raditor. Are you intending to extend the system by T'ing off existing flow/return or just making exiting pipes longer? By cutting and capping you ought to be able to have the CH/HW working as normal (a part from the bit you have isolated).

If T'ing this might not work if using soldered fittings as pipes have to be dry to solder. Could use push fit T's with a capped short bit of pipe in the T. Block the system again when the works are complete, remove the stub, shove in the new section.

[zaax]

Check that there are not already stop valves already in to do this. If not when you drain the system to do this job add some stop valves.

[RobertL]

...or you could insert a couple of full bore taps - much easier to reconnect it all when the work is done.

Robert

[RJS]

I find that a wet-capable vacuum cleaner is an invaluable tool when dealing with rad removal and cutting water pipes.

Richard

[Johny B Good]

Unless you have a need for profligate amounts of hot water (large family obsessed with cleanliness to the point of having at least one bath a day or showering morning, noon and night) the saving realised by using gas over electricity is rather marginal in the summer season when you'd normally have the central heating shutdown anyway.

Considering the extra work involved with most of the offered solutions, I'd have done with it and just use the immersion heater (after all, it's what it's there for!).

[Dave Liquorice]

Can you get full bore push fit? If one or both of the pipe ends starts glugging, pusfit can be shoved on PDQ compared to tightening a compression. B-)

[Fredxxx]

A minor point. But make sure your immersion heater still works before relying on it!

[Peter Taylor]

"Lobster" wrote

With due respect, if you have a pressurised system and you don't know the answer to your own question, it makes me feel you shouldn't be mucking about with it yourself.