Hi,
I have a Vaillant sine 18 T 3 WF H. and the problem is no hot water the symptoms are:-

1, low water flow at the hot taps (all taps in the house are the same).
2, Not enough pressure to fire the boiler.
3, there is plenty of flow at the cold taps.
4, I can get hot water from the taps by running the heating system but still at a low flow rate

I assume there must be a problem at the boiler and I would be extremely grateful for any suggestions

MickH, July 2007

Hi T.h.s

Thanks for the help, you were spot on it was the diaphram (split). There was also quite a bit of calcification in the valve body, so I have cleaned everything up and replaced the diaphram (£2.50) and everything seems to be working fine.

This is the first time I have used this website and I am impressed by both the help and speedy responses I have had.

Thanks again, MickH

MickH, July 2007

The t3w does'nt have a pump speed adjuster only a pump function link wire in the control panel which should always be set to 1.
The fault you are experiencing is almost certain to be that the water section diaphragm is not operating either because it has stretched or split or that (more likely) the water flow rate is too slow. This model has a flow regulator mechanism which is not really adjustable.
Has your water from the hot taps become slower recently?
If yes then try turning the pressure higher on the inlet tap on the feed pipe to the water section .
If water at the hot tap has'nt slowed recently it may be the diapragm.
Either way, the point about the pump being for circulating around the radiators is true of some, but not this one. There is a hyraulic valve on the gas feed pipe that will not open without the pump running so it has to run for both.
To test, turn the hot tap on and listen. If the pump does'nt come on then it is purely a water flow/ diapragm fault.
If the pump does come on and the boiler still does'nt fire (but still works o.k. for heating) then the problem is in the control panel or in the wax capsule of the diverter valve.

T.h.s, July 2007

Hi Russ,
Thanks for the reply. The system is pressurised ok, when I said there was insuficient pressure to fire the boiler for hot water I meant that there was not very much water coming out of the taps The boiler fires up fine when you turn on the radiators. The pump as I understand it is just for circulating the water around the radiators and that works fine.

Thanks again for your help.

m1ckh, July 2007

you could try setting the pump speed to its max.. my vaillant has 1 or speed setting 2 been the fastest.. and the 'not enough pressure to fire boiler' could be that the water pressure within the boiler is too low to rectify this you need to add more water , do this by finding to clod water inlet/supply pipe to your boiler and turn it on. there should be a dial/gauge to show you how much water i pressure is in the boiler mine needs between 1(min) to 2 on the gauge which also has a green line to show this is the optimum amount of pressure any less than the required amount and the boiler will not fire for heating or hot water

russ, July 2007