Downstairs hot tap not firing up boiler.

[denmachan]

Hi, I wonder if anyone could advise?

I have a worcester greenstar junior 28i combi boiler (pretty old - nearly 15 years?)

I haven't really been vigilant with the servicing to be brutally honest. However the boiler seems to have worked well over the years. But now I have a problem.

I recently had my kitchen done up, and the fitter put in a low pressure mixer tap.

The tap, when in the 'Hot' position does not appear to be firing the boiler? It does sometimes, but it's intermittent.

When the tap does NOT fire the boiler, I have found that if I turn on the Bathroom hot tap as well, then THAT will fire the boiler up, and when I turn it off the boiler stays fired up while the kitchen tap runs, and it then works fine!

Obviously running upstairs every time I want hot water in the kitchen is a bit daft, even though it works, but can anyone explain why this happens? is it an easy fix, or do you think a new boiler will be the best solution, given the age of this one?

i must admit, the water doesn't seem to get as hot as it used to, but if it's an easy fix I may persevere but I feel like I may be just delaying the inevitable new boiler.

Any advice would be much appreciated folks!

 

[Gasguru]

Try turning off the cold feed service valve to the tap under the sink...does it make any difference?

 

[denmachan]

Try turning off the cold feed service valve to the tap under the sink...does it make any difference?

Hi, thanks for your reply!

I just tried that. Turned off the cold tap feed via the isolation valve under the sink. Checked there was no cold water on the mixer tap, but still getting a good flow of water from the hot side of the mixer tap. It's still not getting hot though, unless i turn the bathroom sink hot tap on first.

What would turning off the cold feed prove, if you don't mind me asking? I'm a complete amateur so I'm not sure what this would eliminate?

Thanks in advance!

 

[terryplumb]

Sounds like there is not enough flow thru the hot tap to trigger the boiler. Can you measure how many litres the hot only delivers in one minute ?

 

[denmachan]

Sounds like there is not enough flow thru the hot tap to trigger the boiler. Can you measure how many litres the hot only delivers in one minute ?

Hi I just tried this with a 2 litre jug and I'd say it gave about 5 litres in a minute. the thing is, with the old taps, this never happened? The other taps had separate hot and cold taps tho. Would a new boiler deal with this kind of flow rate?

Thanks.

 

[terryplumb]

That flow rate is plenty to trigger your boiler. How does that flow rate compare to other hot taps that do trigger the boiler ?
I would suspect the boilers flow sensor is dodgy.

 

[Madrab]

Is there an isolator on the hot supply under the sink? Is that fully open? Are they connected correctly?

 

[denmachan]

That flow rate is plenty to trigger your boiler. How does that flow rate compare to other hot taps that do trigger the boiler ?
I would suspect the boilers flow sensor is dodgy.

The flow rate is slightly less than the upstairs tap, but not by much? if it was a fault with the flow of the tap, then should the boiler stop burning when I trigger it with the upstairs tap but leave the tap on downstairs? It works fine every time once the boiler has been triggered. It's just the initial start up. I just dont get it!

 

[denmachan]

Is there an isolator on the hot supply under the sink? Is that fully open? Are they connected correctly?

Yes mate, there is an isolator on both the hot and cold feeds, and they are both fully open. Do I really need isolators? The tap is in the kitchen and I have a 'sure stop' switch right next top them if I need to turn the water off. Would removing them completely improve the flow? Or at least the hot tap one?

Thanks.

 

[Madrab]

Not really, not if it is all mains pressure. The ISO's are there if the tap needs serviced, it means the rest of the supply can be left on so always good to have them fitted. Was just in case it wasn't fully on. I guess it's now down to doing a test and see if an open pipe from the hot ISO into a bucket will flow ok and get hot, if so then it's the new mixer tap that's at fault

 

[terryplumb]

When you open a hot tap and a certain amount of litres per minute flows through the boiler ,the boilers flow sensor switch triggers the boiler and it fires up.
5 litres per minute is more than enough to trigger the boiler into firing up ,but it is a very low rate of flow ,probably due to low internal diameter flexible hoses that connect your tap to the supply pipework. Once the boiler fires up with your " upstairs tap" it will continue to produce hot water when your downstairs tap is running even after upstairs one is closed .
You should engage an engineer to check out the boilers operation ,your flow switch should bring the boiler on even with the poor flow of 5 Lt/ min.

 

[denmachan]

When you open a hot tap and a certain amount of litres per minute flows through the boiler ,the boilers flow sensor switch triggers the boiler and it fires up.
5 litres per minute is more than enough to trigger the boiler into firing up ,but it is a very low rate of flow ,probably due to low internal diameter flexible hoses that connect your tap to the supply pipework. Once the boiler fires up with your " upstairs tap" it will continue to produce hot water when your downstairs tap is running even after upstairs one is closed .
You should engage an engineer to check out the boilers operation ,your flow switch should bring the boiler on even with the poor flow of 5 Lt/ min.

Hi Terry, I've just measured the flow a bit more accurately with a 1 litre container. It takes 14 seconds to fill the 1 litre bottle, meaning in 60 seconds I'm getting 60/14=4.3 litres/min. From my (admittedly short) research I'm finding that a flow rate of 3.5 litres/min is AMPLE to trigger the boiler.

Therefore I'm sticking my neck out that this is a boiler fault, rather than a problem with my water supply?

I've made up my mind that I'm getting a new boiler, so could you recommend one that would work efficiently with that kind of flow rate (i.e 4.3 litres/min)

I've got about 2K saved up for emergencies, which I consider this to be. I need reliable hot water and heating, so I'll bite the bullet and get a new one.

I live in a mid terraced house with 3 bedrooms, 7 radiators, and a shower which is fed by the boiler and a bath. We never use the shower and bath at the same time so no issue there.

Any recommendations mate?

Thanks in advance.

 

[denmachan]

Not really, not if it is all mains pressure. The ISO's are there if the tap needs serviced, it means the rest of the supply can be left on so always good to have them fitted. Was just in case it wasn't fully on. I guess it's now down to doing a test and see if an open pipe from the hot ISO into a bucket will flow ok and get hot, if so then it's the new mixer tap that's at fault

Thanks mate. I never even considered that the tap may be to blame!

 

[terryplumb]

The poor flow from the tap has brought the issue to a head. Don't misunderstand me ,the flow rate is very poor ,and obviously less than the previous tap . Nevertheless the boiler should still fire up.
Rather than go to the expense of fitting a new boiler , would it not make sense to repair yours ,and explore why your tap is so poorly performing ?
Can you post pics of tap ,and the plumbing going to it ?

 

[Madrab]

Thanks mate. I never even considered that the tap may be to blame

If it was me, then I'd certainly start at the cheapest/easiest end of the fault finding process. Rule out the one thing that's changed.