Open vented heating and hot water

AJackson

We've just moved into a rented house that has an open vented heating and hot water system. This is new to me, I've always lived in houses with combi boilers since I was little so I might not be understanding how it works correctly.

We only moved about 3 weeks ago and until this week we've had the heating on. It's an ancient looking system with a clock ticking round and 4 pins A,B,C,D where it turns on a A and C and off at B and D. There's no thermostat anywhere in the house although all the radiators have thermostat valves on them.

If I'm understanding it right, there's a boiler downstairs that comes on when the programmer triggers it and heat the tank in the airing cupboard. This then supplies hot water to all the radiators. At the same time, there's a tank of cold water in the loft which supplies the hot taps, via the hot tank in the airing cupboard. If we don't run the boiler everyday to keep the tank hot, there's no hot water.

As far as I can tell, there's no way to turn off the heating and still have hot water, short of going round and turning all the radiators off at their individual valves as I've done. We're then running the boiler for 3 hours/day (1 1/2 hours is the closet the A/B C/D pins will go together) just to get hot water.

This wouldn't be so bad but we use hardly any hot water. The dishwasher and washing machine only have cold water supplies, the shower is electric. We probably use 10-15 litres/day in total and that's generous. It's just using the sink the in the bathroom when I shave, the odd thing we wash in sink that doesn't fit in the dishwasher. There's just 2 adults in the house.

It seems like a complete waste of money.

Am I missing something here? or is it just that these are designed for producing much more hot water? The only other thing I can think is that we just manually turn it on and off for a while each day so it's only on maybe 45 minutes to an hour but that's not exactly practical.

I'm tempted to just live without hot water for the summer months.

Any advice would be appreciated, maybe I'm just being an idiot, I'm used to turning on the tap and getting hot water at any time from the combi boiler.

jk0

I wouldn't stress about it. I'd have thought your boiler's internal thermostat would switch it off once the water is up to temperature.

dominoman

Have you asked the landlord? They really should be able to explain how it all works.

There should be a controller that allows you to select Hot Water, or Heating, or both. Check again on the system with the 4 pins. These are fairly common, and not that ancient.

Can you see a 3 way valve in the airing cupboard? It will often be marked ABC. A is the exit for radiators (A for warming your !!!!) and B is for the Hot Water (B for Bath). If there is one then somewhere there should be a controller that allows the water to flow one way only, rather than both.

Worst case, so long as your hot water tank is well insulated, it isn't going to cost a huge amount to keep it warm.

dominoman

And BTW, for a normal sized house this system works much better than a combi boiler. You have masses of hot water on tap whenever you need it, so in theory you can run several hot showers and taps at the same time without any loss of pressure.

stator

Check out the insulation on the hot water tank. If it's an old system the insulation is probably poor. You can buy a jacket from Screwfix for £10 and wrap it up snug to reduce heat loss.

Unfortunately you do have to heat up the whole tank but it shouldn't take 3 hours to heat up. It should have a thermostat on the side so you can change the temperature of the water too.

Le_Kirk

If you can find the boiler name and model number and post it, there is a large number of knowledgeable people on here who will advise you.

Smiley_Dan

dominoman wrote: »

And BTW, for a normal sized house this system works much better than a combi boiler. You have masses of hot water on tap whenever you need it, so in theory you can run several hot showers and taps at the same time without any loss of pressure.

Which would be fine [see below], except for:

This wouldn't be so bad but we use hardly any hot water.

Heat losses from HWCs are large, and should be at least understood so that better approaches can be adopted in the future.

It's true that combi boilers are not appropriate for large houses with high DHW demand. But that's not the same thing as saying a system boiler is the answer. Standing heat loss is a BIG problem for energy efficiency, and if we as a nation ever get around to fixing space heating, this will be the next thing to tackle.

Other instantaneous solutions include inline modulating electrical heaters.

saverbuyer

dominoman wrote: »

so in theory you can run several hot showers and taps at the same time without any loss of pressure.

Is that not pressurized unvented you're talking about?

Smiley_Dan

No, my guess is he's talking about a pumped vented system with cold and hot tanks.