Help! Central Heating turns on when hot water is turned on..

Postby cez_raf » Mon Apr 16, 2007 5:36 pm

Hi! Hope someone out there can help!

I have a very puzzling problem with the central heating and hot water.

The problem is simple, when the hot water is turned on, all the radiators turn on.

Now the history:

Originally (20 yrs) the system we had was a potterton boiler with a hot water cylinder, cold water tank and gravity fed system. Everything worked fine i.e hot water and central heating was independent. Recently about 6-8 month ago, the problem arised. We assumed that there maybe something wrong with the bolier or hot water cylinder, and we were also in the process of getting a loft conversion. The vendor recommended we get an unvented system (some have megaflow we got a santon premier plus 210 litres) since we would have no room for a tank etc. So we decided to go for it, a glowworm 30sxi and a santon hot water cylinder and all the rads with thermostatic valves. We also have 3.4 bar water pressure.

After they changed the bolier and cylinder we still had the same problem!
Everytime we turn the hot water on, the central heating goes on.

So we called the plumbers (that did the new system) and they diagnosed the problem and said that our original system or circuit was connected wrong and that they could rectify it by bridging or connecting an additional pipe to the primary flow - i dont know the exact details but i can find out and post.

Today, they came round and spent the whole day trying to fix it by doing exactly what they said would fix it, but unfortunately it did not work.

My question is if anyone else experienced the same issue, and if they had theirs fixed? Also, all the zone valves were checked to be working. The thermostat also works, i.e if the central heating is on, and we turn the thermostat down, the heating eventually turns off, but even if the thermostat is down to begin with, and we turn the hot water on, the rads start heating up!

Can anyone help or give some ideas?

Help would be much appreciated!

Thanks in advance!
Posts: 3
Joined: Mon Apr 16, 2007 5:18 pm


Simply Build It

Postby ken » Tue Apr 17, 2007 7:36 am

Wow what a superb message board , right i believe i have the same problem has cez-raf yesterday i knocked the heating off on the timer so i could just have hot water but my central heating stays on !!!
Help needed its red hot in here .
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Joined: Tue Apr 17, 2007 7:32 am

Postby cez_raf » Tue Apr 17, 2007 9:12 am

couldn't view reply?
Posts: 3
Joined: Mon Apr 16, 2007 5:18 pm

Postby cez_raf » Tue Apr 24, 2007 2:46 pm

Hi, I wanted to report that problem is now fixed!

BUT.... my initial suspicion, that everyone was saying was true - the Zone Valve!

The plumbers spent a total of 12 hours trying to fix the problem, over two days. They installed pipes, re-connected the primary flow, and told us so many things related to the existing system, but all failed! They said that a pipe was connected directly to the central heating from the boiler! IDK...

In the end the replaced/fixed the Zone Valve where the hot water splits to the central heating and that fixed the problem! Now they wont get a penny more than £350 which was originally quoted to fix the problem, but i feel annoyed that we kept telling them that we think its the zone valve and they kept saying it was the pipes! We knew that we never had the problem before untill recently and even after they changed everything!

It just goes to show, even with 20 years experience behind them, they can overlook something so simple!

Anyways, out of sympathy, it would be kind to pay them, even though it was their fault in the first place!

My advice to anyone with a similar problem is to replace the ZoneValve first as its the cheapest solution! Then move onto pipes etc...

Hope the above helps!
Posts: 3
Joined: Mon Apr 16, 2007 5:18 pm

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