No Hot water - Please help!!

25 Mar 2008
Reaction score
United Kingdom

We have a problem with our heating system. At present we are only getting luke warm water. The central heating has timers for both the radiators and hot water. When the timer comes on for the hot water the radiators come on.

I assume this is a problem with the valve? There was a clicking sound coming from the cupboard which houses the pump, valve and cylinder, however this now appears to have stopped.

The pump has been replaced twice in the last 18months and the valve once. We have also had the system power flushed about 12 months ago as I was informed that the sludge could be causing these parts to fail.

Any help and advice would be very much appreciated.

Sponsored Links
Possible stuck valve on HW side, possible pipes are blocked with sludge. With hot water ON and heating Off, check the pipe from the valve into the side of the hot water cylinder, should be hot!
Thanks for your reply.

The hot water is on and the heating is off - The pipe which comes out of the cylinder is warm, however the pipe on the other side is very hot. The radiators are also on full whack!
Syncon motor burn out, stuck open for heating ........ maybe, what valve is it you have, honeywell????
Sponsored Links
Syncon motor burn out, stuck open for heating ........ maybe, what valve is it you have, honeywell????

would say stuck in heating position.
but a burnt out motor won't cause that.
more like a jammed shaft or ratchet in the actuator.
The valve has SUNVIC on the top and is a 3 port valve. As posted above I did originally hear a clicking noise which has now stopped. Is the likely to be the motor?

Is this something I can do my self, or should I be getting someone in?
clicking can be the ratchet inside.

take the top off and watch the valve when you operate it.
also you can isolate the fused spur and get the valve into its relaxed position and check the lever on the end see if its floppy or has resistance.
So take off the white box - do i need to shut off water or electrics to do this?

also you say watch the valve when you operate it. So do you mean I can turn the heating on while the top is off to see what it is doing?

What is the fused spur?
The Sunvic's aren't very spectacular, soon replaced mine with a Honeywell. I checked it thoroughly, when removed from the system it seemed to work as it should, once replaced and system filled, I was back to the initial problem, couldnt get the hot water circuit to work without the radiators coming on too. Valve was allowing flow to both ports, regardless of system requirements. Have a look here:

The fused spur is the switch that isolates the power supply to the boiler and system.
thanks for your replys so far.

I have taken the sunvic white box off the base plate and have managed to move the copper valve with my hand which has give us hot water back.... thanks god! If i just replace the white box say with a honeywell rather than the entire valve which I think is beyond me, do you think this may work?
you cant mix and match valves. If you can turn the spindle by hand the most likely problem you have will be the actuator is broken, did you watch the drive, "D" shaped hole in bottom of white box, and alter controls - HW on, CH on, both on, both off etc?
thanks Mick. I did not look at the bottom of the device as I was watching the motor itself which did nothing when I alternated the hot water and radiators on and off. Unfortunately one of the wires snapped off the motor when I was trying to disconnect it so I can not put it back together to see!

I have found a identical white sunvic box which looks like I can just attach it to the base plate and then wire it up. Do you think this may solve the problem given I could turn the spindle with hand?
An identical sunvic sd 2751 actuator will set me back £110 which I will have to try and fit myself.

I have been quoted aprox £150 to come a fit a honeywell from a heating engineer. Any suggestions on which way to go?

The fitting of the new actuator seems quite straight forward. I fit it to the base plate and spindle and then wire it up to the white panel on the floor, copying the wiring of the old one! Or am I gonna end up in a mess and better off just getting it done properly?

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links