Worcester Bosch 28i Junior

30 Jun 2006
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United Kingdom

Help pls. We\\\'ve just moved into a house with the above boiler system and it is taking some getting used to cf conventional boiler system.

We have a bath with the usual bath taps which are interconnected with a shower system (hose, shower head and mixing system) for showering in the bath tub. The problem we are facing:

We cannot get the boiler to supply hot water when we turn the shower system ON. Hot water only comes up when the hot water tap for the bath is ON (takes a few seconds) - and when this happens, we divert it to the shower system by turning it off with the shower system remaining opened.

Even then, after doing this, the water goes cold after 2-3mins when we have to repeat the process again ie turn the hot bath tap On to allow water to flow back through it when it takes a few more secs (approx 15s) before hot water is back in business.

This trick has worked so far but is a pain - it leaves you cold in between spells of hot water with you playing with the taps.

Any comments/advice much appreciated.

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Sounds like the flow is too low for the flow switch in the boiler to recognise reliably.
SOme areas had had their pressurs dropped, and Worcester have mailed corgis on how to take flow restrictors out of their boilers...
What IS the flow rate in litres per minute from the shower, on hot alone? Measure into a 9 litre bucket, say.

COuld be a faulty FS too of course.
It may still be under the warranty. The hot water demand should switch it on with about 2.5 litres per minute flow rate.

Its not an engineering solution but your shower may work better if you turn on the basin hot tap with it.

Try changing the shower head with one that allows more water to pass through. Some of the shower heads have very fine holes (usually for saving water) they often get used for crappy electric showers, as they can never heat up enough water to make the shower worth getting wet for. It's like showering under 'gnats pee'.

In other words, try increasing the flow.
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Thanks a lot for the advice and comments.

As I thought and as you all mentioned, it has something to do with the water flow rate - before writing to you guys I already noticed that the hot water to the shower system turns cold less often at certain times of the day eg daytime shower compared with evening - 6-10pm when it cuts off 3 times on average for a 10min shower.

ChrisR - Give or take, flow rate when the hot water Shower system is on is 4 L per min compared with the hot water tap for the bath tub which gives 15 pints of water in 45sec (11L per min). Unless my calculation is incorrect, what a big difference!

I have tested the bath tap water to see how long it remains on Hot for (cf Hot water for shower system), and it does so continuously....
So, definitely, the flow rate from the mains is dramatically reduced when it gets to the shower system.

And so, apart from trying to change the shower head and see, is there any other solution, eg adjustment to combi boiler?
How do I find what flow rate is required to trigger the boiler? (Although this question is pointless as we know there is a problem with the flow rate from the shower head.

Thanks in advance!
Is it a flexible silver pipe from the bath mixer valve to the shower head?
If it is, these pipes only have a plastic membrane/tube inside. They sometimes get twisted and reduce the flow along the pipe.

Has a previous handyman shut off the hot water to the shower via an in-line stop valve and not opened it fully. Check the obvious.
The pipe work to the bath and basin taps are ok, it must be only a small amount of pipe work to find that is feeding the shower if it is on a separate supply!
Sounds almost exactly like the problem I'm having with my Worcester 240 - and after searching here I've come to the conclusion that its probably my divertor valve that's become leakly.. have a search on the forum and you'll see what I mean about the diverter failing.

FYI, The taps for the bath tub are connected to the shower mixer system where the shower hose is originates from. The shower mixer system is fixed to a tiled wall.

My guess is the 2 pipework is connected somehow and involves a valve that automatically diverts to bath taps when both the bath taps and shower system are Open/On.

Anyhow, I will check underneath the bath tub to see what the pipework is like and report back.


Thanks Vamos
Vamos , WB Junior's don't have a diverter valve.

There won't be a valve, the resistance if you're getting only 4l/min will be so high that no flow will go up the pipe!
4 l/min is precisely what you should expect from a head designed for an electric shower.
Try unscrewing the head to see if that's the restriction. If not, unscrew the hose and direct the water into the bath with a jug or similar.
You should get 8 l/min fronma 24 and 10 l/min from a 28 - can;t see the title as I type... There's a flow restrictor in the boile which youmight want to take out if yor water pressure's low.

Having said that, the (filter and)flow switch in a Junior should operate well below 4 litres/min. It's next to the flow switch turbine device, which you could take out and check for blockage/free running. Takes about 1-2 minutes!
Neither the shower head nor the shower hose are the problems re flow restriction
as am still getting 4l/min

As you said, ChrisR, the boiler should still operate at this flow rate...
Is your advice easy to action for a DIY amateur like myself - just don't want to make the situation worse than it is?

By the way guys, is the water flow rate into my house from the mains suppose to fluctuate depending on the demand of the people in the locality?
If not, then, the boiler performance should not be affected by the time of the day one uses the hot water.

Also, does the fact that I have a combi boiler affect the size or the type of radiators that I need - am asking because I planned to update one or two radiators in the future....

If the flow is not restricted by the hose/shower head/inline valves etc and it's the same as a Greenstar 28i junior------------The flow sensor, flow restrictor housing and filter should be perhaps taken out examined for blockages and cleaned.

Drain domestic hw, disconnect electrical connection to the turbine, remove spring clip (moving brass pipe to one side).
withdraw the flow sensor and filter from the housing.

Using the cartridge tag, withdraw the flow restrictor housing. If the regulator housing has become stuck, a pair of long nosed pliers may be used to grip the housing.

To refit, follow the above in reverse, ensuring any seals that have been disturbed are renewed.

The flow sensor is located just above the pump to the right.

This is literally copied from the manual.
As my pseudonym suggests, try it and see.

(I note that the boiler has a choice of two flow regulators i.e. 8 litre and 10 litre. I presume the boiler must have been set up correctly at first installation).

One other thing, and only guessing, does the shower mixer valve have a cartridge type fitting in it - debris in cartridge filter perhaps.
DIYm1 said:
ChrisR - Give or take, flow rate when the hot water Shower system is on is 4 L per min compared with the hot water tap for the bath tub which gives 15 pints of water in 45sec (11L per min). Unless my calculation is incorrect, what a big difference!

I've just tested mine (28i Junior)

It works quite happily down to below 3 litres / minute
Hi all - apologies for the late feedback.

We have managed to resolve this problem - at least, probably temporarily.

By serendipidy, we discovered that the shower water stays hot when the hot water bath tap is partly opened. So, to keep the boiler operational, we leave the bath hot water tap opened just for the water to trickle and divert the water via the shower hose by opening the shower system fully.

I frankly don't know where the problem lies (any ideas) but it works.
hi just read your query if the tap is not a thermostaic type then you may be getting push back from the cold water into the hot as the hot is reduced in pressurer after passing though the boiler. ans is to put a pressurer restrictor on the cold water or chang the tap to a thermostatic one.

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