Heating radiators and cylinder at the same time?

qsk

I have a S-plan set up (2x2-port valves + Honeywell junction box) at home so that the boiler heats radiators as well as an indirect unvented cylinder. I have always set up the timers so that the boiler only heats one at a time. Now it is cold and sometimes it is a pain to sit in cold waiting for the boiler to heat the cylinder. So the questions:
1) does it work if I set the timers so that both the radiators and cylinder are on at the same time? Does the junction box work in an exclusive manner so that only one source is heated like the combi boiler?
2) if the answer the above is yes, is there any ill side-effect, eg, is flow through each circuit going to be significantly decreased causing malfunction of the boiler? The system is a sealed pressure one.
Thanks in advance.

Paradigm

I have a similar setup & I don't have any problem with heating the radiators & hot water at the same time. I don't see why you should.


Why not try it?

greenbee

Paradigm wrote: »

I have a similar setup & I don't have any problem with heating the radiators & hot water at the same time. I don't see why you should.


Why not try it?

Same here.

Le_Kirk

As stated, absolutely no problem with cylinder and radiators at same time however, you may notice a reduction in available temperature as the boiler has to heat water which is flowing through the radiators and the heating coil in the cylinder. I set my system to heat the water whilst I am still in bed and then (with a 10 minute overlap) switch the heating on and the water off in time for the house to be warm when I get up.

qsk

Thanks all for sharing your experience. Certainly gives me confidence.

Le_Kirk, I'd love to have an arrangement as yours - my problem is that the whole family prefer to have shower in the evening. If I heat the water in the morning, there might be heat loss after the length of time... Btw, when you said "a reduction of available temperature", do you mean the temperature of the boiler, or water in cylinder? Also, with both circuits working at the same time, flow is divided and hence only half in each circuit. Will that cause any problem, in particular, to the boiler?

Paradigm

I think he meant that as the boiler is heating two circuits it would take slightly more time for the radiators to reach full heat output.
It also means that the boiler will run for longer instead of cycling until the hot water cylinder has reached the correct temp, this shouldn't take that long.

C_Mababejive

The thing to do is set the system to heat the water when you are in bed/likely to be out at work.

taxspider

I've found this thread whilst looking for the answer to the question of whether it is cheaper to have the hot water on at the same time as the heating, and now I have more questions!

We are on mains gas, have a regular boiler, but it has a funny system whereby the hot water is heated by the returning radiator water in a tank in the basement and then the hot water is pumped (possibly gravity fed) up to a second cylinder upstairs, which is where the hot water is drawn from.

We worked on the assumption that it made sense to heat water and radiators simultaneously as the boiler is already hot and it would only use marginally more gas, but now I've read this thread I'm not so sure.

I infer so far that the boiler prioritises water to the radiators and so the hot water takes longer to heat up when they are on together.

The last comment was to put the hot water on before the heating comes on, but to a layperson that sounds like using more gas because the boiler is on for longer.

But does that actually mean the hot water heats up quicker because the boiler is only focused on that task, and thus it is more efficient?

Additionally we have two water thermostats, one on each cylinder. During the summer we use the immersion on a timer, which is in the upstairs cylinder, and the water seemed hotter than it does now. My OH turned up the thermostat on the tank in the basement and now the water actually seems cooler. I am therefore wondering whether the hot water only goes upstairs once it reaches the required temp downstairs. Now that the thermostat is set higher, it will take longer for the water to come to temp, so maybe turning it up was the wrong thing to do.

Totally appreciate that all systems are different (ours is just weird - old house, old system, relatively new boiler at 9 years old) but if anyone can advise I would be grateful.

There is just the two of us and with a cylinder we heat way more water than we use so I'm keen to keep costs down. We have electric showers, small electric water heater in the en suite as it was simpler than re-routing hot water pipes across the house when we installed the en suite, and we never use the bath. The only time we use hot water really is to wash up, but we have a dishwasher so only need to wash a few things. Ideally we would redesign the system but that would be prohibitively expensive and we would never financially recoup the cost.

Thanks