DIY Doctor UK DIY Forums

Help needed,
Can someone please help shed some light on this quirk I have?
I just bought a house and noticed this quirk. The gas boiler heats water for the hot water tank for the bath etc and radiators for heating the house.
The boiler has two switches that turn the hot water on/off and heating on/off. Each with its independent on/off times. It also has ON/OFF and 1 hour ON function.
When ever I switch on the hot water (ON) but not the heating (OFF) the radiators still come. Even when I turn the thermostat to 10c and I know its warmer in the house.
If I turn the heating ON and the hot water OFF the thermostat works and keeps the temperature to the set point on the thermostat. The hot water remains OFF.
Is there anyway that i can have the hot water ON and the Heating OFF
and hot water has priority when Heating is ON? Is this a silly question?
Any help is much appreciated.
Cheers
Vinny :x :x :wink: :wink: :wink: :wink: :wink: :wink:

The 3 port valve has a motorised valve fitted to the top - this will need replacing also check spindle on valve is free to move.

Thanks for the reply.
What is a 3 port motorised valve and where do I find it?
Can it be replaced by myself?
Are all the valves of the same type? Like what do I need to check to buy a replacement?
Do I have to drain all the water?
Sorry to ask all this questions.

By the way, I am not sure if this helps, the boiler is on ground floor and hot water tank on first floor.
Thanks

An interesting problem and at first I agreed with htg engineer but as I look closer it does not all fit in. One you can select central heating only that means not Y plan. Also W plan would give either or so not W plan. This leaves C or S plan and neither use three way valves. Can’t see it being S so I will plum for C plan. And looking at the plan if one of the micro-switches were to stick on in the motorised valve then yes this scenario could happen. Which means htg engineer was right after all but will be a 2 port valve not 3 port and the 2 port valves come in a number of versions you must make sure it has a change over switch in replacement unit. As to who is right that is very easy how many pipes go to valve 2 or 3. I will watch to see if I need to apologise to htg engineer? PS I am an electrician so look at things different.

ericmark - from reading your post it seems to suggest that with a 3 port valve you cannot have Central Heating on by itself ? unless i have mis-read it.

The whole point in the 3 port valves was for energy efficiency, so that if you were not using the hot water you could have central heating on without heating the hot water.

You can have
CH only
HW only
CH & HW

wow-- I am really confuses now. I don't know anything about Y, W, S and C plan.
All I know is that my boiler has on/off timer and 1 hour override control for hot water and heating separately. i.e I can have HW or CH or both ON at the same time. Also I can have HW and CH OFF completely.
I looked around the hot water tank (since I couldn't see much on the boiler unless I unscrewed the panels). I found a white rectangular box with 4 cables coming out of it (some disappearing under the floor boards) and one going to a small box mounted on the pipes near the hot water tank and another cable going to a thermostat on the hot water tank. The small white box says Sunvic SD1701 and T52 Ts93 backplate. The pipes that are connected to the small box is like a 'T' 3 pipes connecting to it. I hope this is the 3 port valve. If not where else can I find it?

Assuming it's the 3 port motorised valve then what's the best replacement for it.
I have not checked the spindle (?) as I am not sure if I have located the unit yet.

Thanks again for you help

Yes that is the 3 port valve - remove the head to see if the D shaped aperture turns.

If you're unsure get an engineer in

Sorry my apologises, re-looked at my notes, there should be a connection from programmer domestic hot water off to the satisfied on the tank thermostat which also connects to the grey on the valve. Many systems in this area had this link between the programmer and tank thermostat missing, and the programmers had the dip switch and physical stop set to 11 rather than 16 programs mode. I jumped in with both feet and forgot this was a Persimmon Homes special and in most cases full 16 programs is available sorry.

is the valve ticking when you try to get hot water only

Sorry ignoring your problem. The valve has three positions. Non energized gives hot water, half energized give both, full energized gives central heating. Even is it can't return to non energized position with hot water off the boiler with turn on and off and control central heating. So one of three things has gone wrong.
1. Valve stuck and can't return to fully closed.
2. Micro-switch stuck and it is being held electricialy open.
3. Some one has manually moved the bleeding leaver and latched it to mid position. (If it has one)
If it does have a lever by trying to move it you may be able to work out which of the three has happened. The moving of the bleeding lever is sometimes used a quick fix and you my find once you release it central heating stops working. But latching it again will temporary get it working again. If you get same make as already fitted often you can replace one half without the other. Often you can get micro switches from Maplin but with some of the valves they all spring apart when you try to repair them so unless your very able I would replace the faulty half.

Dear all,
Many thanks for the help. I found that the spindle on the valve was stuck. I undid the motor controller and checked what happens when I have
1) HW only
2) CH only
3) HW and CH On (then turning the room thermostat on and off)

I noticed that the motor turns the spindle collar turns in all instances to what's required.
I noticed that the valve spindle position for HW only did not match the motors spindle collar.
When I turned the valve spindle with pliers, the spindle was a bit stiff but with a bit of force it turned. That seemed to free it.
But now water leaks (drop at a time) from the spindle. Shame after all the investigations and managing to fix the problem I got a new one. Looks like I have to replace the whole valve. I called the manufacture and they told me what part I needed to replace the valve. Incidentally just the valve repair kit was nearly as expensive so I had the whole valve replaced. I know know what to do in the future.
I certainly have learnt a lot - MANY THANKS to all of you.
Vinny

Thanks for the feedback - glad this forum helped.

There's many posts that we respond to and we never get a reply or any feedback - it would be nice if people let us know when the problems were sorted, if we were right in our diagnosis and if not did any of the information we gave help in any way.

We can't get it right everytime - until you see the fault, boiler, pipework it's all guess work. But I think most of the time, someone in the forum gives the solution.

Glad we were of some assistance