Posted by: @suzer

@kev-m 

 

We had hot water on all the time when we moved in and got hot water whenever we needed. However it cost a lot of money!  So we only heat once & have circulation pump timed to come on when we are likely to need it. What I don’t know is can you have circulation pump on all the time but the actual heating of the water once? 

I think I've reached the extent of my knowledge on hot water, pumps, etc. (which hasn't taken very long).  Maybe if you started another thread and described your system and how it works someone like @derek-m or @alex-morrow could help. 

Posted by: @suzer

@kev-m 

 

We had hot water on all the time when we moved in and got hot water whenever we needed. However it cost a lot of money!  So we only heat once & have circulation pump timed to come on when we are likely to need it. What I don’t know is can you have circulation pump on all the time but the actual heating of the water once? 

What is the distance from your hot water cylinder to the tap in question?

As Alec stated, a circulation pump is used to pump the hot water from the cylinder, around a loop, and back to the cylinder, unless water is drawn off via a tap along the way. Obviously, if any of the pipework in the loop is not adequately insulated then energy will be lost and will need to be replaced.

Do you know how many kWh's of energy were being used for DHW on a typical day?

2kWh and is timed 6-7.30am.  The circulation pump is off save for 5 mins at 7.30am for the shower and again at 10pm hence we have no hot water when washing hands, washing dishes. There is hot water left in the tank by end of day & we can get it by pressing a boost which activates the circulation pump.  The boyfriend thinks too costly having circ pump on during the day with hot water sitting in pipes going cold unused. It’s an inconvenience that’s all. 

@suzer 

If you know when you will need hot water, then just press the boost a few minutes prior, any warm water in the pipes may not be wasted, since it may be contributing to home heating. It would probably be more economical than a hot water tap, which uses direct electricity.

I have this issue at our property running a secondary return for instant hot water. 

Our house is quite large with long pipe runs from the unvented cylinder to the showers/taps. If I leave the secondary return running all day the efficiency of the unvented cylinder drops through the floor as there is so much pipe work in the house that isn't properly insulated so it loses so much heat cycling it around the house. I've set the secondary return to run from 6am to 9am now so that when we get up we have instant hot water on the showers/taps. It also comes on again from 5pm-8pm for washing up/showering. The only downside is that when someone showers outside of this window it can take over a minute to deliver hot water and we often get spikes of freezing cold/very hot water for the first couple of minutes as it clears the sitting hot/cold water in the system before a constant flow of heated water reaches the shower.

Reducing the amount of time the secondary return ran significantly cut our hot water costs. In an ideal world the unvented cylinder would be centrally located to avoid needing a secondary return or very well insulated pipework if you do need one.

An idea you might want to try experimenting with is rather than run the secondary return pump for several hours at a time, or boosting the system minutes before expected use, is to have the secondary pump turn on for 2 minutes each hour. (I use a programmable plug timer)

As you can imagine, as the pump is turned on it should take a minute or so to flush the pipework loop, so the cold water in the pipework is pushed into the DHW heating tank and is replaced with the hottest water available from the top of the tank.

The pump turns off. Any taps/showers/bath drawing hot water will now have full access to the hottest water available.

Depending on how quickly the water in the pipework loses heat if not drawn from a tap, what might happen is say someone opening a tap 50 minutes after the last pump cycle might get luke warm water. In which case you could try running the pump for 2 minutes every 30 minutes.

Also you should check that the white expansion vessel is plumbed into the cold inlet pipe and not the hot outlet of the DHW tank as mine originally was. This changed my getting hot water from 60 seconds down to 10 seconds.