When my central heating (but not hot water) is turned on there is a brief ignition of approximately 30 seconds
before the ignition stops and an error message of S.53 appears, that is (according to the manual), 'appliance is within the waiting period of the operation block function due to water shortage (VL - RL spread too big)'. The boiler can remain in this state for up to 30 minutes
before it successfully ignites and appears to work.

This problem occurs whether (a) the central heating has been off for some hours, typically overnight, or (b)
when the central heating has been off for some minutes, typically when the living room has reached the temperature dictated by the room thermostat and the room temperature has then dropped and so the boiler tries to get going again.

The problem does not occur when the hot water is turned on immediately prior to the central heating being turned on.

So far I've had (a) new pump fitted and (b) new heat exchanger fitted. But problem continues.

Any help/ advice gratefully received.

Mary Jane, January 2009

central heating working fine but when tap is opened dhw comes out hot then after about 5 second temperature starts dropping & dhw getting cold.

TASH, February 2015

I don't know !!!! but I am having numerous problems with our boiler. Had no hot water all Xmas and new year, plumber replaced 2 new pumps plus other parts. Finally got hot water back but faults keep returning (F-81 & F-91) have to reset to fix this has now led to our heating staying on through various raidiators which I have to turn off manually as not going off when our Digistat+2 iflo timer states !! Any ideas are welcome !!

Rhian, January 2013

the heating symbol on my viallant ecoTech 937 plus boiler does not appear so the central heating is not working at all! I have tried turning the boiler off and on but a s.24 error appears before changing to a s.30 error but the heating symbol never appears. the hot water is working perfectly and I have emptied all the radiators in the house of water until there is nothing but air left but this has still not resolved the problem. any suggestions on how to fix the problem are welcome!

Jesse, April 2012

I had this same problem on a vaillant, its nothing to do witht the boiler but the installer who has oversized the appliance, the temperature differencial between the flow and return is to hign so if u ( like said in the other post) reduce the kW rating this changes the temperature differencial

piddy gas, February 2009

Thanks Tony.

Turning d0 down from 18kw to 9kw had certainly helped.

Mary Jane, January 2009

I saw this and it might help you. It is also happening to my at the moment with my brand new Vaillant 438.
Tony

Hi Everyone

Hope this post helps someone else and cuts short the time taken to resolve this problem. Thanks to all of you that offered your help and suggestions.

Originally I posted a problem topic:

Vented System - Reverse Flow - I think ?
http://www.diynot.com/forums/viewtopic.php?t=150534

To cut a long story short I introduced multi-zones (2 x CH, 1 X HW) which when a single CH zone was open caused the boiler to shut down after a short while indicating code S.53 - Appliance is within the waiting period of the operation block function due to water shortage (VL-RL spread too big)

I called out a Corgi Plumber but although he made suggestions to change pipework and spoke to Vaillant he was honest and said he wasn't sure it would resolve the problem.

I decided to phone Vaillant again today and had a protracted discussion with Vaillant Installation Helpline - it was suggested I change the d.0 'Heating part load' setting to 27kw. This had been factory set at its max - 38kw. I was then told to slowly increase the value ensuring all zones worked independently and am currently at 34kw without any re-occurance of the S.53. on any zone. It would appear that the boiler needs calibrating to operate with the smallest zone whilst still offering a high output to cater for when all zone valves are open. Being set at max 38kw appears just too high when only one valve zone is open.

Tony McCormick, January 2009