Increasing hot water pressure, combi boiler

[alphonso]

Hello

I'm still trying to get more hot water pressure from the combi boiler. I've been told that if I change the pipes from the mains (out under the pavement) to the boiler, that should increase the pressure significantly.

It's a Victorian house, I think with old lead piping from the mains to the cellar, and copper 15mm pipes from the cellar to the boiler.

Has anyone done this with any success? ..or have anything to say about it.

Many thanks

[robinhood21]

If the old lead pipe is scaled up then it could make a difference. I too live in London (north) with lead pipe from road to kitchen and the pressure is fine. First thing would be to check that all the cocks are fully turned on (including the one in the road, pavement, or garden) as, I have known folk to turn down the pressure to stop being splashed when turning the kitchen sink tap on. If you hold your finger over the kitchen tap, can you hold back the water or does it squirt everywhere?

[alphonso]

The cold water pressure is actually pretty good, there's no way you could hold back the flow with your thumb. The hot water pressure isn't too bad either but I'm installing new bathroom with a cloud shower and want to get the best out of it.

I was told that the hot and cold pressures should be the same as the mains feeds into the boiler. This isn't the case. Perhaps the boiler can't heat it quickly enough and partially closes an internal valve?

[C&C]

When we moved into our current house, the water pressure and flow of the cold water was really slow. We were thinking about putting in a big tank and a power shower as we do not like weedy showers. We were advised first to try replacing the pipe from the mains into the house. It was old lead piping and was replaced with new UPVC/plastic or whatever it is (you can tell I'm not technical!). Anyway, water pressure/flow increased so much that we had to have a restrictor put on to slow it down a bit.

We put in a new combi/instant boiler with a decent capacity, and people who visit think we have a power shower except the tank never runs out - which is both good and bad. Good - potential for a nice long shower / convenience and bad - bills - potential for a nice long shower!

In your situation, you may get a different result. It will depend on your local mains pressure. Your old piping may or may not be a bottleneck. The best thing to do would be to speak to some of your neighbours - ideally if any of them have had their pipe from the mains replaced, they would be able to give you an indication. Even if some of them have a fairly old pipe which is not very restrictive, if they are getting good water pressure/flow this would be an indication of what you could expect.

It would probably be a good idea to replace the pipe anyway, as I believe that having old lead pipes carrying your water is not ideal?


ETA - Having seen your post re. cold water pressure/flow is OK, it would suggest possibly your boiler not being able to keep up, or there's possibly a restrictor limiting flow through your boiler? Both should be the same?

Edited by C&C on Thursday 3rd September 12:22

[Goochie]

What type/specification of boiler is it? It could simply be that you're boiler has a deliberate restriction in place because it wouldnt be able to heat the water if it were flowing through at full pressure.

My money is on the boiler being under-spec for the job.

[Deva Link]

alphonso said:

I was told that the hot and cold pressures should be the same as the mains feeds into the boiler. This isn't the case. Perhaps the boiler can't heat it quickly enough and partially closes an internal valve?

If the cold pressure and flow is OK then there's nothing wrong with the supply pipe.

As others have mentioned, the hot water flow is probably restricted in the boiler due to its rating.

[alphonso]

...it's a worcester junior installed 2 yrs ago. I thought it might not be up to the job but the shower room is right above the boiler. If nothing else is running in the house, it should be plenty for a really strong shower.

Thanks for the ideas, perhaps the boiler is faulty?

[Deva Link]

alphonso said:

...it's a worcester junior installed 2 yrs ago. I thought it might not be up to the job but the shower room is right above the boiler. If nothing else is running in the house, it should be plenty for a really strong shower.

Thanks for the ideas, perhaps the boiler is faulty?

So there's a 24i and a 28i version of that boiler - which have you got?

Hot water flow rate is 9.8 (24i) or 11.4 (28i) litres per minute. Measure your hot water flow rate. Should more or less fill (or easily overflow if it's a 28i) 2 gallon / 9L bucket in 1 minute.

ETA: I should add that's for a 35C temp rise - so you really need to measure the incoming cold water temp and the hot water temp. On my FIL's boiler mentioned below, now it's fixed the hot water is certainly too hot to put your hand under.


My FIL has an older version of this boiler and his hot water flow was OK but the temp was pathetic. Turned out the diverter valve in the boiler was faulty and it was heating up the rads when he asked for hot water.

Edited by Deva Link on Thursday 3rd September 13:39

[headcase]

I too have the same boiler and have also had to replace the diverter valve for basically not turning on when i turned the hot tap on but opening 2 hot taps allowed it to switch on, when i took it apart the rubber in the diafragm had just disintegrated causing the fault, all parts avaialble via ebay . Im sure you can adjust the hot water pressure via a valve in the boiler, have a look throught the installation manual thats came with it, if you can adjust it then it will be in there.

[Deva Link]

headcase said:

I too have the same boiler and have also had to replace the diverter valve for basically not turning on when i turned the hot tap on but opening 2 hot taps allowed it to switch on, when i took it apart the rubber in the diafragm had just disintegrated causing the fault, all parts avaialble via ebay . Im sure you can adjust the hot water pressure via a valve in the boiler, have a look throught the installation manual thats came with it, if you can adjust it then it will be in there.

I didn't see it myself but my FIL is very mechanically minded and he said changing the diverter valve was a pretty complex job.

The flow seems to be set by using different coloured restrictors. Certainly in his, the flow was a lot greater than it was rated which I was a bit baffled by (if it's restricted) but of course the water temp drops as the flow increases.

[Big Al.]

We have a combi installed a few years ago, earlier this year the hot water pressure in the upstairs bathroom started to slow, cold was fine . We had the boiler checked out and all it needed was a new washer in the hot supply filter, as this had started to deteriorate and clog the filter.

[alphonso]

I think the hot water pressure has been the same since installation. Maybe I'm expecting too much! It's certainly not enough to run two showers at the same time, and it's mediocre with just one. I'll ask the installation plumber to come back and see what he thinks. Many thanks for your input.