Hot water taking a long time to come out of tap

dharm999

We changed our boiler to a system one, and the water is now at mains pressure.  We also took the opportunity to put in a larger hot water tank, and relocated it next to the new boiler rather than being in another room about 10ft away from the boiler.  Old boiler was a traditional one, and we had a water tank in the loft, now redundant.  The problem we have now is that it can take a couple of minutes for hot water to come out the taps, whereas previously it came through in a few seconds.  Spoke to my plumber who said the only way to improve things would be to run a pipe directly to the taps we want hot water to come quickly from, which to me, sounds strange.  Previously there was a pump in the set up, but no pump now, is it possible to put a pump on the hot water pipe coming out the tank, to get water quicker to the taps?

I really thought by moving to mains pressure we would improve things, and the water flow has improved but it has meant waiting a lot longer for hot water.  Is there anything i can do to improve the situation?

FreeBear

If the pipes from the tank go through a tortuous route, and are substantially longer than the old pipework, it will always take time to get hot water out of the tap. Putting a pump on an already pressurised system isn't going to help much. When the new tank was fitted, was new pipework laid in to the taps ?

I had a new combi boiler fitted last year, and got rid of the old unpressurised DHW tank that was in a bed room. Opted to install the boiler directly below the bathroom, and get near instant hot water there. In the kitchen, I still need to run the tap for a few minutes - Two reasons for this. A longer run of pipe, and a limited flow from the tap (~7l/min). The bath tap has a flow of ~10l/min in comparison.

victor2

Quite possibly a lot of the old pipework has been used, so the hot water is going a long route between the tank and the tap. New pipework taking a shorter route will be the only answer.
Like @FreeBear, we had an old hot water tank removed and a combi boiler installed. The boiler is physically not far from the kitchen, but it takes forever for hot water to come through as it goes upstairs through the old pipes then comes downstairs through more old pipes before it reaches the kitchen tap!

ThisIsWeird

Yes, this doesn't make sense!

Your system running at mains pressure should provide a faster water flow. So, Q1 - how 'fast' does the water come out your hot tap? If you could place a pan under your hot tap and open it fully for 10 seconds, and then 'times' the number of litres in the pan x 6, you'll have 'litres per minute'. NB - the water doesn't have to be 'hot', just flowing out the hot tap.

It would also be useful to know what your incoming mains flow rate is like - do you know if this was measured? It should have been, before a plumber recommends changing to a pressurised - unvented - system.

How much visible plumbing is still in the old hot cylinder's location?

Albermarle

Exactly the same happened to us when we switched from a traditional set up, to system boiler/unvented cylinder.
I always assumed it was connected to all the rerouting or pipes that was necessary, as already suggested.

dharm999

I may have not been very clear.  The new hot water cylinder is on the ground floor, about 10ft away from where the old hot water tank was.  This was in the kitchen in an alcove (no idea why but that’s where it was, it was there when we bought the house).  New pipes were run from the new hot water cylinder location to where the old hot water tank was.  Given the extra distance, isn’t that far, is it right that it can now take at least a minute for hot water to come through the kitchen taps, when previously it was nowhere near that time.  Is there any answer other than re-routing pipe work?

dharm999

Also, to clarify, the new boiler is in the same place as the old one.

ThisIsWeird

You have been clear, although the additional info is useful.
The reason I ask about your offending hot tap's flow rate is to try and determine whether the cause is a lack of mains supply, or an excessively long pipe.
Since you have a stored water system and not a combi, there should be no delay in getting the hot water moving - Ie, the boiler doesn't first have to fire up to provide this. So, it's all down to the passage of time it takes for the DHW to exit your tank, and crawl out yer spout.
And a minute sounds excessive. TWO minutes is ridiculous! I guess my bathroom tap takes around 30 seconds to provide good hot water from my combi, but it's at the opposite side of the house, and the pipe runs via the loft.
So, did your plumber test your mains Flow and Pressure before accepting that a change to 'unvented' was fine?
What IS your rising mains flow and pressure? Do you know?
Could you try the flow measurement rate I suggested, please, at both your kitchen cold, and bathroom hot?

ThisIsWeird

To explain some other points you've pondered, yes, converting to mains - provided the mains supply is adequate - does away with the need for a pump. 
No, you cannot really improve matters now by the use of a pump unless your incoming mains is truly pitiful. You are only permitted to boost your incoming mains to a max of 12 litres per minute, and - to be frank - if your mains was less than this, then your plumber should not have recommended the change to 'unvented', imo.
You can super-boost your mains supply to pretty much any level you like, but this requires a storage accumulator as well as a more powerful pump. It will still only take the max 12lpm from your mains, but after storing it in the accumulator, it can then supply your house at awesome rates. 
Three things can affect the time it takes for hot water to pass through your pipe. One is obviously the pipe length, but it's hard to see that this has changed that much. Another is the pipe diameter, and good chance yours is 22mm, whereas mains ('high') pressure systems can cope with narrower, eg 15mm. 22mm pipes hold a lot more water, so this extra volume needs to be first shifted before the hot appears. And the third is the flow and pressure driving the water through the pipe.