Can't get a hot bath suddenly

[d000hg]

Last couple of days I can't get a hot bath even if I run only hot water AND turn the tap a bit shower than normal.

The water is pulsing got to warm every 5 or 10 seconds. We have a big Combi boiler and I've checked it is not overheating and cutting out because we had that issue before with a heat exchanger blocked up. But that was running hot for maybe 20s then going stone cold, not this weird fast alternation especially as the tap is 20s+ from the boiler.

The boiler reports a constant temperature... So what could it be THIS time? We already had to replace both heat exchangers and it's getting expensive...

 

[gasbanni]

It's obviously a boiler fault, do you have the same problem just running basin a hot tap ?

You need to get a decent heating engineer out, if you leave a tap running and go to the boiler is the burner constantly on or does it go on and off ?

Best I can come up with not knowing the boiler make and model.

 

[terryplumb]

Do you have a Thermostatic mixer valve /tap of any description on the bath taps or the supply to the bath taps ?

 

[d000hg]

It's obviously a boiler fault, do you have the same problem just running basin a hot tap ?

You need to get a decent heating engineer out, if you leave a tap running and go to the boiler is the burner constantly on or does it go on and off ?

Best I can come up with not knowing the boiler make and model.

I'll test other taps, the shower is not having issues.

My one thought was, how do boilers know to prioritise hot water over heating? I know mine does and assume that's typical but how is it controlled and could there be a fault?

I only ask because I noticed the radiator in the bathroom remained red hot while running the bath... It's been cold at night with the heating running full blast.

I think we got a free year boiler cover when we switched to BG, time to dig out the details before I call the regular plumber!

 

[picasso]

Sounds like the diverter valve may be stuck, run the hot water and see if the heating pipes under the boiler get hot,

 

[gasbanni]

On the old systems the bathroom radiators used to be on the cylinder circuit ....so they'd heat up when the cylinder was heating up for hot water ........

With the heating completely turned off run the bath hot tap if the towel rad gets hot it's plumbed in wrong !

The boilers have priority hot water they're designed that way don't concern yourself over it.

Turn the towel radiator off only on one side and see if you still have hot water coming out of the tap. You never know !!!!!

 

[gasbanni]

Sounds like the diverter valve may be stuck, run the hot water and see if the heating pipes under the boiler get hot,

Hey there Picasso didn't you used to be in Lincoln area ?

 

[d000hg]

On the old systems the bathroom radiators used to be on the cylinder circuit ....so they'd heat up when the cylinder was heating up for hot water ........

With the heating completely turned off run the bath hot tap if the towel rad gets hot it's plumbed in wrong !

The boilers have priority hot water they're designed that way don't concern yourself over it.

Turn the towel radiator off only on one side and see if you still have hot water coming out of the tap. You never know !!!!!

That's interesting but the system is relatively modern and I am fairly sure it (used) to work as it should... if I started the bath running then turned the heating on to heat the bathroom up, the radiator would not get hot until I finished running the bath.

I might repeat this test, I need to make sure the radiator's are not hot before I start though!

I understand the boiler gives priority to hot water, but I was wondering how this works and if it's something that could fail? Is that the diverter valve @picasso is mentioning?

 

[terryplumb]

Do other hot taps ,kitchen sink ,bathroom basin etc ,give constant hot water ?
Can you post pic of bath tap ?

 

[picasso]

Hey there Picasso didn't you used to be in Lincoln area ?

Hi gasbanni no I have lived is Essex for around 40 years, I don't think I have ever been to Lincoln.

 

[gasbanni]

Hi gasbanni no I have lived is Essex for around 40 years, I don't think I have ever been to Lincoln.

Well your lucky then !