Heatline boiler, hot water slow to come through.

[Click4]

Hi, just wondered if there are any known causes for hot water to be slow to come through from a combi boiler? It's a Heatline C something or another lol.

But when you turn on the hot water taps on the bathroom basin which is only say between 1-2 m away in physical difference, pipe length will be longer, it takes quite a while for the hot water to come through, in some cases a minute. Or is this normal?

Reason I'm asking is because, would like a thermostatic mixer shower, and don't need a pump as its a combi boiler.

But because of the time it takes for hot water to come through its leaning the descision more towards electric shower... But it wouldn't have as much pressure. But if I can find out the problem with the hot water (if a problem exists then it will make the power type shower more viable.

 

[Agile]

There can can be many causes.

A simple check is to actually measure the time before the water from a tap gets hot.

Then repeat that by holding the hot water out pipe on the boiler.

Tony

 

[Click4]

Hi,

Had a brainwave earlier, will check it later.

I think, whoever plumbed it in.... rather than connecting hot water out on boiler to the hot water pipe by the bathroom and feeding entire hot water pipework this way and cap off the pipe where hot water cylinder was.

I have a feeling that they have instead... taken a pipe from the boiler, all the way to the back bedroom where the hot water cylinder used to be... and connected it up there.

So effectively, the hot water has to flush through a good 7-10 metres of cold 22mm pipe water going towards back bedroom to where cylinder used to be... then flush another 7-10m of cold 22mm pipe water coming back on itself again towards the bathroom. as much as 15-20m of pipework in 22mm filled with cold water to get to the bathroom which is located right next to the boiler.

 

[Agile]

Reusing 22 mm pipework is going to increase the time to get hot.

Combi DHW outputs should always be in 15 mm.

Will also increase gas and water useage.

But sometimes getting a direct connection from boiler to taps is a problem.

Rarely used but a radial star connection method is best but only usually possible with new build or complete refurb.

Tony

 

[Click4]

Right, just spent some time doing some investigation into this.

Think I have now (hopefully) sussed it out, scrap above... wasn't correct.

Out of boiler, is 15mm, this goes under the upstairs hallway floor, into the bathroom, then it goes into a 22mm pipe behind the bath panel... so effectively, 15mm pipe feeding a 22mm pipe... this 22mm pipework is the original pipe work from when it was a gravity fed tank system.

1 side of that 22mm Tee with 15mm feeding into it, goes right towards basin and bath, other side goes left through the wall towards where hot water cylinder used to be located.

Logic would dictate, that the water from boiler should come down the 15mm pipe, into the T, then turn right and come out of the sink... that's what would be expected.

But feeling the pipes what is happening with tap running and cold hot water in the pipe is actually that, hot water from boiler, feeds into the 22mm, but instead of going right towards the open tap, it is flowing left towards where the hot water tank used to be which is flushing the cold water out of all of that pipework..so until all the cold water is gone from the pipe the opposite side of the T doesn't start warming up.

Maybe, its because the sink basin is reduced down from 22mm to 15mm at the tap, so the route of least resistance is in the opposite direction?

Either way, not correct for a 15mm pipe to feed a 22mm pipe, and as mentioned a 22mm pipe will hold more cold water anyway and take longer for the hot water to displace it.

But on top of that, this system is doing funny things with water going in opposite direction to where its required which is flushing entire pipework out.

 

[Agile]

I don't think that anyone ( not even you ) will be able to understand your last sentence!

Tony

 

[Click4]

what I meant by it, apologies lol, is

Water comes out of boiler, through a 15mm pipe.

it goes to a T under the bath which is 22mm pipe and original pipework.

But instead of the hot water going right at the T towards the basin taps... it is flowing left and forcing all the cold hot water out the pipe from the opposite direction. Don't know why, it sounds silly to think that.. but that's what is happening.

Basically turn on the basin tap, and all the pipework running towards where the hot water cylinder used to be becomes hot first, then the pipe running towards the basin becomes hot last.



obviously not an accurate representation in terms of what bends / restrictions and lengths the pipe consists of... but that is how the water is flowing through the pipes towards the basin... looks odd I know that inside the same pipe the water is flowing in 2 directions.

But open opening the basin tap, I can absolutely say that the 15mm feed pipe started becoming warm, then the pipe running left became warm, and pipe running right became warm last.

 

[Click4]

Just thought I'd update this,

The pipe work running to the bath and basin has been cut out in the photo but was where it is capped off.

Had to cut the pipes because somebody run them inside the bath legs making bath removal impossible without cutting the pipes.



The boiler cold water feed is fed from the red handle valve.

Hot water from boiler is 15 mm pipe next to it which fed into a 22mm pipe which the. Run 3m to back bedroom where hot water cylinder used to be.

Cut everything out, re-plumbed cold to boiler and hot from boiler in 15mm using more direct pipe work with less restrictions and lagged the new hot water pipe and what an improvement, hot water still takes a few seconds or so but much quicker, better flow and pressure and hotter.

 

[Click4]

Didn't want to create a new topic for a related topic.

Same boiler, still hot water problems.

Comes through a lot quicker now, and pressure is a lot better also.

Cold water static pressure is around 4 Bar.

Hot Static is the same.

But dynamic pressures cold drops to around 3 bar.

But hot is dropping to around 1.8 bar? At one point I tried it and it dropped as low as 1.5 bar which is under half the static pressure.

Want to fix it as I think I'm getting slight cold back feeding on shower mixer due to hot dropping to 1.5-1.8 bar and cold only dropping to 3 bar... Yes I can fit a non return valve and was even considering fitting a PEV but in my mind hot and cold pressures should be pretty similar on a combi.

There was a half bore isolator on the boiler cold feed but had removed this. Pressure was visually higher but that was all done before testing.

So either some kind of restriction through boiler or problem with it? It does go hot and cold sometimes which I know is due to sludged heat exchanger. Doesn't do that as much though since removing the isolator though... But clearly something is still restricting the pressure inside the boiler.... Any suggestions?

Thanks

 

[Click4]

Think ive hopefully figured it out.

Had a look for a filter on the boiler cold inlet, couldn't see one, only a flow restrictor which is expected.

But did notice the cold water in and hot out on the boiler use half bore isolation valves.. this would of been how it was manufactured.

So, probably what is happening is, with shower on, the cold water being higher pressure than the hot is creating a venturi effect which is trying to suck the lower pressure hot water through the hot water pipes.

But due to the 2x half bore isolators on the boiler and built in flow restrictor the water cannot refil the hot water pipes quick enough which would explain the roughly 2 bar drop in pressure on hot water side, whereas cold is only exhibiting a 1 bar drop roughly in pressure.

Obviously the flow restrictor is required for correction heating of the hot water, but might try and switch out the factory half bore isolators for full bore ones if I can source them and see if that improves it.

Along with fitting a Pressure Equalising Valve to stop the venturi effect occurring.