Help - binary gas flow on Hot water

[MacroPhotoFly]

Summary - The gas seems to come on full to heat hot water, gets to a temperature then turns fully off, restarting moments later when (obviously) the water has dropped in temperature. Hence the hot water in the pipe goes up and down temperature like a yoyo. Water temp is very hot (>65 degs) when at peak of cycle. Gas flow or water temp doesn't seem to be regulated by water temp switch on front of boiler (i.e. water temp not kept constant by gas flow adjusting)

Details - I have a Worcester 28 CDi combination boiler (suspect around 7-8 years old, we've only been in the property 4 years) in a 4 bed house with one bathroom. Direct cold water mains feed to the boiler. We didn't really notice the problem with the hot water until the shower got upgraded although it was there on every tap (just thought thats how the bolier works, on/off to regulate the temp) if you just ran it hot. Shower works great and pipework is fine for it (i.e. we considered the right shower head for likely flow, etc), but the problem with heating (of water going binary on/off) is a lot more obvious now and you can hear the pipes expanding/contracting the whole time the shower is running.

So for my questions, if anyone can please help
- Are boilers meant to work like this or should they adjust flame to keep water at constant temp?
- If not what is likely to be wrong?
- Is it just time to get a better boiler with a bit more "poke"?

Note - Boiler was "serviced" by BritGas 2 weeks ago who gave clean bill of health despite my wife pointing out this problem (and occasional drip of water from underneath) - yes I know they only check to see if gas is pouring out the side of it and don't fix anything else (strange if I take my car for a "service" they identify all faults and offer to fix)

 

[doitall]

Is it a thermostatic shower.

make/model is.

Are there check valve on the feeds.

Is it connected the right way round.

Don't sound as though it's been connected too well.

 

[MacroPhotoFly]

It is a thermostatis shower (I'll dig details out later) but the problem exists on all hot taps (i.e. run a hot tap, it goes very hot, then cools down, then heats up, then cools down, etc).

The other thing I would note is that the hot taps need to be on high flow before the boiler kicks in (i.e. if you don't have the tap on a high flow the water remains cold)

 

[Legion]

So for my questions, if anyone can please help
- Are boilers meant to work like this or should they adjust flame to keep water at constant temp?
- If not what is likely to be wrong?
- Is it just time to get a better boiler with a bit more "poke"?

`Binary` hot water explanation would help me out,

 

[kevplumb]

`Binary` hot water explanation would help me out,

a brain larger that a dehydrated pea would help you out






op

sounds like a lack of boiler modulation the flame should adjust to the load

 

[MacroPhotoFly]

Sure - binary in the sense the boiler seems to be 'on' or 'off' (cycling between those states) when the hot water tap is flowing , rather than moderating the gas flame to keep a constant temperture to the hot water.

 

[bengasman]

Sounds like a classic example of a sludged up heat exchanger.
How did you managed to find out about the burner staying on full? If I have the correct boiler in mind, there is only a tiny little peephole to show the flame.

 

[MacroPhotoFly]

Can't confirm it is actually on full, I admit. But through peep hole I can see burner comes on and stays at that flow until the point it turns off completely - then cycles between those two states (plus the fact the water goes burning hot, when "hot water temp" dial is on lowest setting)

 

[bengasman]

Cycling when in dhw mode is almost always caused by a blocked secondary heat exchanger.
That in turns means most of the time that the whole installation is soiled and thus needs cleaning, very common problem.

You will find helpful additional info in FAQ.

You may get "advice" from legion, be aware that he is a troll purporting to be a RGI, but doesn't actually know what he is talking about.

 

[Legion]

a

brain larger that a dehydrated pea would help you out

Funny innit, everyone else is ok to abuse willy nilly (poor willy) if that was me i would be threatened with a ban or it would be removed by Mod with big large warning for all to see. Funny old world.

 

[Legion]

You may get "advice" from legion, be aware that he is a troll purporting to be a RGI, but doesn't actually know what he is talking about.

Grow up. You are beginning to sound as bitter as Kevplumb.It`s a giggle fellah.

 

[kevplumb]

a

brain larger that a dehydrated pea would help you out

Funny innit, everyone else is ok to abuse willy nilly (poor willy) if that was me i would be threatened with a ban or it would be removed by Mod with big large warning for all to see. Funny old world.

so press the button and report it then

Quote:
You may get "advice" from legion, be aware that he is a troll purporting to be a RGI, but doesn't actually know what he is talking about.


Grow up. You are beginning to sound as bitter as Kevplumb.It`s a giggle fellah. icon_wink.gif

it might be to you

i don't think the op thinks it's funny

 

[doitall]

Can anyone feel a £7000.00 BG powerflush coming on

 

[kevplumb]

and sec h/x oh and the flow swich is iffy

the diverter might be clogged

why don't you have a new boiler as well

View media item 14445

 

[Legion]

For those who care: Binary means something made up of or based on 2 things, gas is made up of 6 constituents, Methane, Ethane, Nitrogen,Propane,Carbon dioxide and Butane. Can`t remember percentages of each, definitely not binary. Seems the dehydrated pea has had a little drinky poo.