Instant 105e Upstairs rads get hot when preheat turned on

[Backboiler]

Also system pressure loss (PRV leaking). Been twice before to recharge PV. Are the two issues linked or do we have two separate problems? I suspect div valve passing when DHW on preheat. Can anyone tell me which seal will need replacing?

 

[IDCHAPPY]

The water must be passing through the diverter valve dude, it's the only way rads should get hot on hot water/pre heat mode.

 

[diamondgas]

:iagree: however if the phex is restricted you'll get the same symptoms! 🙂

Regards re-charging, on these bad boys the diaphragm on the expansion vessel can perish with all that heat and flow kicking about in it! Weird set up!

How do you recharge the PV? May be a daft question but not all folk are made aware of what it is they're doing in my experience and tend to close off the system when re-pressurising! 🙂

 

[Backboiler]

:iagree: however if the phex is restricted you'll get the same symptoms! 🙂

Regards re-charging, on these bad boys the diaphragm on the expansion vessel can perish with all that heat and flow kicking about in it! Weird set up!

How do you recharge the PV? May be a daft question but not all folk are made aware of what it is they're doing in my experience and tend to close off the system when re-pressurising! 🙂

I drain the boiler by opening the drain, leaving it open while connecting my foot pump to the Schrader valve. I pump it up to about 1 bar and leave it for a few minutes to check there is no drop, close the drain then refill the system pressure. leave the foot pump attached to check the vessel pressure matches the system pressure before removing the foot pump.

So its a dv valve service kit including the plunger?

 

[Backboiler]

The water must be passing through the diverter valve dude, it's the only way rads should get hot on hot water/pre heat mode.

Thank you
Will it be the DHW section or the bit behind (pressure differential)?
part num 248727 or 248728?

 

[diamondgas]

I drain the boiler by opening the drain, leaving it open while connecting my foot pump to the Schrader valve. I pump it up to about 1 bar and leave it for a few minutes to check there is no drop, close the drain then refill the system pressure. leave the foot pump attached to check the vessel pressure matches the system pressure before removing the foot pump.

So its a dv valve service kit including the plunger?

Spot on, regards re-pressurising! I hope I didn't offend by asking, I've seen so many close off the system then re-pressurise!

Regards the service kit, I believe it comes with all the guts 🙂

 

[RoryD]

:iagree: however if the phex is restricted you'll get the same symptoms! 🙂

Regards re-charging, on these bad boys the diaphragm on the expansion vessel can perish with all that heat and flow kicking about in it! Weird set up!

How do you recharge the PV? May be a daft question but not all folk are made aware of what it is they're doing in my experience and tend to close off the system when re-pressurising! 🙂

That's right, I seem to remember that the preheat uses the Expansion vessel, not sure of the set up but it would be the first port of call. There's water loss from prv would indicate a common denominator there

 

[bewsh]

Did you clean out or replace the PRV when you sorted the expansion vessel? There could be a bit of sludge on the seating causing it to pass.

With regards to the radiators heating with the pre-heat, you can just replace the one section of the diverter valve, pretty easy to change.

 

[Backboiler]

Did you clean out or replace the PRV when you sorted the expansion vessel? There could be a bit of sludge on the seating causing it to pass.

With regards to the radiators heating with the pre-heat, you can just replace the one section of the diverter valve, pretty easy to change.

The PRV wasn't passing after re-charging the vessel so I left well alone. Regarding the section of the diverter valve............. Which section would require replacing? Is it the vertical section, complete with brass plunger underneath the motorised head or one of the larger rubber diaphragms. I think there are two of these. One for the HW and the other for CH.

 

[diamondgas]

The motorised valve decides where the water is diverted to, the diaphragms detect flow! If you're replacing the 'guts' then replace what you can, usually the valve 'head' and the front valve and spindle..... If my memory serves me well?