Weird HW problem

[gasjunkie]

Hi guys.

-Small flat with a kitchen and one bathroom.
-Vokera Unica 32 BHE boiler.
Problem: Kitchen tap has low HW pressure and sporadic hot temp

• It's sporadic so sometimes water comes out piping hot, other times the boiler won't fire
• Diverter motor and valve checked and ok
• Bathroom sink tea and bath has HW whenever tap opens.
• Kitchen tap is one metre from boiler, bathroom is three metres from the boiler.
• Doesn't seem to matter if CH is firing or not. CH works absolutely fine.
• adding: Changed kitchen tap, worked fine for 15mins then back to sporadic running cold

I am thinking about changing the Plate Heat Exchanger.
But when it does fire the temp is excellent. Bathroom HW flow and temp are good though.
The bathroom HW does not point to the Plate HE.

So pretty confused here, any thoughts appreciated.

 

[ShaunCorbs]

Change the kitchen tap but have a look at the flexis if it has them kinked ?

 

[gasjunkie]

Change the kitchen tap but have a look at the flexis if it has them kinked ?

thanks and I should have mentioned - I changed the tap today!
worked better for 15 mins so I thought I'd cracked it.
then it dropped flow rate and started running cold again.

 

[gasjunkie]

good point about the flexis

 

[John.g]

If you open the bathroom hot sink tap while kitchen hot tap has low flow/temp is the bathroom tap flow/temp ok and does the kitchen tap still have low flow but hot water?.

 

[gasjunkie]

If you open the bathroom hot sink tap while kitchen hot tap has low flow/temp is the bathroom tap flow/temp ok and does the kitchen tap still have low flow but hot water?.

Yes correct JohnG

 

[John.g]

As suggested, maybe flexi kinked/damaged so swap hot/cold if cold flow was ok.

 

[gasjunkie]

As suggested, maybe flexi kinked/damaged so swap hot/cold if cold flow was ok.

I'd be unlucky to have had a kink on old tap and new one but it is possible... Will check that...

So maybe not the plate HE? Shower is running hot so if it was the plate HE, I'd have consistently low flow, low temps... Is this right?

If so, then pipework as you guys say... Maybe the ballofix under the kitchen tap? Do they ever go wrong? I've never had one go wrong, anyone else?

I'm wondering about debris ? Like just before the ballofix. Suppose I could whip it off and check.. But the boiler has several filters for the HW...

 

[ShaunCorbs]

Not the boiler if no other outlets are having the same problem

 

[Aquarius]

Failed check valve at shower?

 

[gasjunkie]

ok good and makes sense ShaunCorbs ..

Trying to pinpoint and understand the connection between low flow and low temp:

one thing I noticed today after the new tap went on - I was checking HW on, off, swing the mixer H to C and back and it was behaving well for about 15 mins as mentioned above.
Then I as I was watching it the flow rate dropped noticeably. Then it started running cold.

Would low flow rate be low enough not to fire the boiler?
This would explain lack of HW. It runs cold. not warm.

 

[gasjunkie]

Failed check valve at shower?

ok thanks - how would that affect the kitchen tap?

 

[ShaunCorbs]

Yes low flow = boiler not making hot water as it’s not sensing demand

 

[Aquarius]

ok thanks - how would that affect the kitchen tap?

Cold can push the hot out of the way.

 

[gasjunkie]

Cold can push the hot out of the way.

sure I kinda understand that but if the shower is not being used, the kitchen tap is still having the problem. could the check valve still affect the kitchen tap if shower not in use?

 

[John.g]

Did you change a mixer cartridge or do you have separate hot and cold taps to the dual flow mixing spout?

 

[Aquarius]

could the check valve still affect the kitchen tap if shower not in use?

Yes it could. Isolate coldfeedunder boiler, run hot water, any water come soon out, likely check valve failure

 

[gasjunkie]

Did you change a mixer cartridge or do you have separate hot and cold taps to the dual flow mixing spout?

old and new tap are both mixer, not dual flow mixing spout