No h/w from Vallaint 242 - is it the pressure diff switch?

[Aulus]

I'm frustrated - can anyone please tell me if I'm on the right track?? British Gas seem to disagree

I couldn't get hot water through my (new) thermostatic mixer shower when turned down below about 35degrees. Also the hot water generally would sometimes not come on, but was sometimes OK if the CH was on.

A British Gas engineer visited, changed the boiler's diverter valve.

It's better, but still sometimes not switching on. BG say its either my shower or local water pressure. Either way nothing they will fix.

I think (I'm guessing, I'm not a heating engineer) it's the pressure differential switch - when I turn the hot water tap on, the plunger doesn't move, but if I turn it on sharply, SOMETIMES it does. Same with the shower - sometimes it works if I turn heat up full, but not always.

 

[Rob]

This a vuw 242? i get confoosed!

TBH the diverter should have cured the problem you are refering to as this is also the differential switch.

Have you/they measured the flow rate of the HW when it doent switch on?

is it just the shower it gives the problem?

 

[Aulus]

Yes, thanks, its the TurboMAX VUW 242E

I thought it was the mixer at fault, so this morning as a test I turned kitchen tap on gradually until full flow acheived - about 7 l/min - boiler didn't come on. Did it again but turned tap on sharply - hot water DID come on.

BUT - I repeated this & it didn't work. So it is an intermittent fault. I also tried to get hot water out of the bathroom basin tap, & as its a lever I put it instantly full on - nothing but cold water.

The part I'm referring to is this:

http://www.heating-parts.co.uk/Product.asp?Prd=268235

The white nylon plunger is meant to rise & release a microswitch when tap is on. Sometimes it does, sometimes it doesnt.

I'm convinced this is at fault.

 

[Gasguru]

Did BG change the whole diverter?

Ie the diaphragm in the lower section, the bow (white plastic lever that actuates the hot water switch) and the switch itself. All these items can cause intermittent hot water.

Once the pump is running the differential pressure switch is then activated to prove the pump is funtioning. The water needs to be free of air so check the auto air vent is ok and the system pressure is 1 Bar.

 

[timmy74]

Yes, thanks, its the TurboMAX VUW 242E

I thought it was the mixer at fault, so this morning as a test I turned kitchen tap on gradually until full flow acheived - about 7 l/min - boiler didn't come on. Did it again but turned tap on sharply - hot water DID come on.

BUT - I repeated this & it didn't work. So it is an intermittent fault. I also tried to get hot water out of the bathroom basin tap, & as its a lever I put it instantly full on - nothing but cold water.

The part I'm referring to is this:

http://www.heating-parts.co.uk/Product.asp?Prd=268235

The white nylon plunger is meant to rise & release a microswitch when tap is on. Sometimes it does, sometimes it doesnt.

I'm convinced this is at fault.

thats the pump proving switch, this will operate or lift when the pump runs.. normally a blocked weep tube, diaphragm in switch faulty or faulty pump.

 

[Aulus]

Hi Gasguru

Here's as much detail as I can think of:

He fitted a whole new brass assembly/housing so I suppose he changed everything

The auto vent cap is open but I don't know if the float/valve are OK, as I cant get the top off.

I can't test the pressure but I've just checked the flow rate at downstairs kitchen sink, & the bathroom basin upstairs - hot water is 8.5L/min, cold is 12.6L/min

If it's relevant water comes out the shower at 5.5L/min

Also I just ran the hot water at kitchen sink at a slow rate of 3.5L/min, & the boiler didnt come on. But it used to come on at that rate.

UPDATE - I just repeated this last bit and it DID come on, then the flow gradually slowed until it stopped altogether!!!

Anything else I can check?