Hot water going cold

[Jbcory74]

I’ve just had a gas engineer/plumber round to take a look at the boiler. He tested it and said the issue is quite unusual. Typically, when there’s a problem like this, it’s usually down to a faulty fan. In most cases, you’d notice that the fan doesn’t operate properly when there’s low flow going through the boiler. However, increasing the flow rate usually kick-starts the boiler into working.

But in our case, it’s doing the opposite — the boiler isn’t starting with high flow, but it does work on a lower flow. He said our boiler is more than capable of handling a fast flow. In fact, we should be able to run both the kitchen tap and the bath at the same time without any issues in terms of pressure or performance.

He’s going to speak to the boiler’s manufacturer to get some advice, as he doesn’t want to just start replacing parts unnecessarily. As for the ensuite, the mixer tap, and the valve — he doesn’t believe they’re the cause of the problem.

 

[Johntheo5]

I would suggest getting someone to have a look at your shower, there should be non return valves at th hot&cold supplys which might be difficult to access but if so or even firstly I would switch off the boiler, isolate the cold water into the house, switch on the shower to drain off any water, remove the mixing bar on the front, blank off the hot and cold supplies, and do a few tests again, that will rule the shower in/out of the problem.

 

[Jbcory74]

Thanks! I’ve just sent him the message he will speak to manufacture tomorrow and be coming back up!

 

[Jbcory74]

He said

“No problem, happy to try anything if it's going to work!!!“

Will keep you updated. Thanks everyone so much!

I would suggest getting someone to have a look at your shower, there should be non return valves at th hot&cold supplys which might be difficult to access but if so or even firstly I would switch off the boiler, isolate the cold water into the house, switch on the shower to drain off any water, remove the mixing bar on the front, blank off the hot and cold supplies, and do a few tests again, that will rule the shower in/out of the problem.

 

[CountryFan]

I’ve just had a gas engineer/plumber round to take a look at the boiler. He tested it and said the issue is quite unusual.

Really???

Typically, when there’s a problem like this, it’s usually down to a faulty fan.

Not that I’ve heard of before - sounds utter nonsense imo.

He said our boiler is more than capable of handling a fast flow. In fact, we should be able to run both the kitchen tap and the bath at the same time without any issues in terms of pressure or performance.

I highly doubt that being a combi, but happy to be proven wrong.

He’s going to speak to the boiler’s manufacturer to get some advice, as he doesn’t want to just start replacing parts unnecessarily.

Ok, we’ll see what they say hopefully if he will divulge and similarly yourself

As for the ensuite, the mixer tap, and the valve — he doesn’t believe they’re the cause of the problem.

Quite a common problem, but then again I’m only on a forum, not site.

 

[Jbcory74]

Unusual, because he said if the fan (not a fan) but the spinning thing) is faulty, usually it stops working with low flow and gets kick started with a fast flow… but ours is the reverse… working with low flow but not with fast…

I’ll let you know and try take notes as he’s speaking!

 

[CountryFan]

Just for shíts and giggles: I attended an apartment complex this morning for the same issue, albeit on a hiu, isolated the cold going in and water evident at the kitchen tap. I couldn’t isolate the hot to the mixer and it stopped, so it wasn’t that, so passed back to our plumbing department to rule out the shower and basin.

 

[CountryFan]

Unusual, because he said if the fan (not a fan) but the spinning thing) is faulty, usually it stops working with low flow and gets kick started with a fast flow… but ours is the reverse… working with low flow but not with fast…

I’ll let you know and try take notes as he’s speaking!

Unless he’s on about the flow sensor/turbine?

 

[Jbcory74]

Yeah that lol

Unless he’s on about the flow sensor/turbine?

 

[Jbcory74]

But if anyone has ideas for his next visit let me know!

He didn’t go upstairs (my little one was going to bed) but did say about the mixer shower being isolated when off anyway, and not always possible to isolate it any other way…

I can ask this again when he’s here day time!

 

[Johntheo5]

But if anyone has ideas for his next visit let me know!

He didn’t go upstairs (my little one was going to bed) but did say about the mixer shower being isolated when off anyway, and not always possible to isolate it any other way…

I can ask this again when he’s here day time!

The outlet from the mixer is isolated but if the thermostatic mixing valve hasn't returned to the fully hot position (allowing no cold water to pass) and if the HW non return valve is passing then cold water pressure can interfere with the boiler DHW flow so IMO requires isolation one way or the other.

 

[Jbcory74]

Thank you. I’ve just copy and pasted your message to him! He said yesterday he is happy to test everything as long as he can get it all working!

 

[Johntheo5]

Any update on your problem?.

 

[Jbcory74]

He came last night…

Isolated the shower but we still had an issue with the flow being unable to be on full without it going to 00 and not firing up the boiler.

So then he completely turned all water off, and slowly reintroduced it back in while running the hot water tab to make sure that flow was adjusted - he thought maybe the main flow was set too high??

Anywho… the flow seems better… and the hot water was working…


But then mats night I had a shower in the en-suite and the water took an age to warm up - like it was freezing cold for say 2 minutes. Never used to, I used to just turn it on and get straight in because the wait wasn’t long for it was warm up…

Anywho, when showering the water mid way through ran cold for 1-2 minutes then went back warm again…


He’s told me now to use the main bathroom shower only for a couple of days to see if it is the shower that is faulty…

Any update on your problem?.

 

[Johntheo5]

If he isolated the shower, ie so that the cold&hot water couldn't mix then looks like a boiler problem even though very strange allright that a higher flow rate would cause a flow switch/turbine problem, if that is the problem.

Its strange that he says the shower may still be faulty (and only use the main bathroom shower), if the shower has/had been isolated properly and the problem still persists then surely it can't be that shower thats the problem?

Just to be clear, can you open the valve fully if you use the main bathroom shower only.

The only "problem" with a high boiler DHW flowrate is that the HW temperature can be too low, easily increased by reducing the shower or tap flowrate.