Hot water only working occasionally

nuttyphilt

Hi,

Don't know if there's any plumbers here who could help me. I've had a couple of plumbers come out to my house and currently feel like I'm a bit in the dark so could use some advice (and hopefully save some time and money!).

Basically we moved into a house a couple of years ago that's been refurbished. It's got a new boiler, controller & radiators but the old hot water tank. I had a guy come round a couple of months ago to service the boiler and he noticed that the immersion heater was switched on (presumably since day one of us moving in...) so switched it off. Since then the hot water has been sporadic and I've had a plumber round to look at it who's puzzled by it all...!

This is a list of points that might or might not be relevant::
1. Hot water heats up sporadically (i.e. sometimes it's hot, sometimes it's luke warm) so we're pretty much still dependent on the immersion
2. When we want the heating on, we have to switch the hot water on too. As far as I'm concerned they should be separate because we have a 3 port valve.
3. When the heating is on, it'll only go off with the hot water, i.e. if the heating program switches off but the hot water program is still on then the heating stays on
4. There's no thermostat on the hot water tank (not sure if this is a problem though...)
5. I just noticed that when I switched the hot water on only, then the control codes on the boiler (Vaillant) were showing the heating codes, e.g. S.4, S.7
6. Controller is a Honeywell ST9400C with wireless thermostat . All seems to be working fine on the face of it.

So far the plumber has changed the 3 port valve which hasn't solved anything. Next thing he's proposing to do is put a thermostat on the hot water tank, and fit a new controller. He says everything points to the controller being the issue.

Does anyone have any ideas what our problem could be? Starting to go mad with it all!

I notice in the Honeywell user guide that there's reference to switching it to a 'mini programmer' where heating & hot water are more closely controlled with each other. Could this help us?

Thanks in advance.

G_M

Of course it needs a stat on the hot water cylinder.

the boiler (Vaillant) were showing the heating codes, e.g. S.4, S.7

It's not a combi boiler that's been fitted is it?

ps - I hate to think what your leccie bills have been!

I suggest you post over on the DIYNot forum here. Lots of heating experts. Make sure you include the make and model of each and every componant as well as the symptoms.

nuttyphilt

Does it definitely need a stat? I googled (obviously I'm not a plumber!!) and there was mixed results - some people said if you don't have one then the boiler regulates the temp.

No, it's a Vaillant Ecotec Plus 428.

Re: electricity bills. I guess we just paid what we paid but definitely looking forward to a reduction!

J_B

nuttyphilt wrote: »

He says everything points to the controller being the issue.

That's my thought too.

Son in Law is a sparky. Friend of a friend had a problem that the plumber coundn't sort ... sparky sorted it!!

nuttyphilt

So do you think it's worth explaining it all to an electrician and seeing if they reckon they can fix it?

greenbee

Definitely worth getting an electrician to look at it. My controller was wired wrongly (by the plumber) and it caused all sorts of issues. Took the electrician about 5 minutes to work out what was wrong and not much longer to fix it.

matelodave

You should have a thermostat on the tank as well as a room stat. Are you sure that the three-port valve is working properly and wired correctly - has it got auxiliary contact to fire the boiler and run the pump.

The three-port valve should be sending hot water to the heating or hot water tank when the appropriate item calls for heat - if the tank hasn't got a stat then it can't operate the valve, nor can it fire up the boiler or pump so it's probably only operating when the heating is on.

It's probably not actually the programmer thats the issue, it's probably just wired up incorrectly

As the programmer has a 7 day funtion is there a randomness bwteeen the days and on/off times.

Is the wireless stat also programmable, if it's worth checking that it and the programmer aren't switching at different times.

Has the thing been wired correctly to switch the heating and hot water independently - hard to do if the tank hasn't got a stat.

Some older programmers would only switch the heating on if hot water was called for and you might find that this is how this one has been wired.

A lot of plumbers aren't ever so good at the leccy side of the controls and don't wire them correctly especially if something has been replaced.

So you really need to make sure that all the components are working correctly and that the wiring is OK. Make sure that the set times aren't conflicting and switching stuff off when it should be on and vice versa.

nuttyphilt

Sorry for not replying (life got a bit busy the last few days!) but thanks for the advice.
All the programmer and wireless stat functionality seems correct. I've double checked it all and can see things being triggered when I expect.
My suspicion is the wiring like you say. Now to find a good heating electrician... Any recommendations for someone in SELondon??

G_M

nuttyphilt wrote: »

Does it definitely need a stat? I googled (obviously I'm not a plumber!!) and there was mixed results - some people said if you don't have one then the boiler regulates the temp.

How can the boiler regulate the temp of the tank if it does not know what the tank temp is?

The stat is there to tell the boiler "I'm cooling down. Please switch on and heat me up again". Or "I'm hot enough. Please switch yourself off or divert to the central heating!"


The presence of a hot water tank suggests the answer to this, but please cnfirm, as requested, whether or not you have a combi boiler? Your problem may be connected to incompatibility........

nuttyphilt

Just to follow up on this...

I found a great heating engineer who resolved the issues. Basically he fitted a thermostat on the hot water tank, replaced the 3 port valve with 2 separate valves (one for hot water, one for heating) and rewired the controller (which he said was wired completely incorrectly).

All working perfectly now!

Thanks all for the advice.