radiators getting warm with the hot water


Postby kenny bush » Sun Jul 10, 2011 12:55 pm

Hi all. Hope someone can help.

I've just installed a new, oil fired heating system. Its a Grant Vortex Eco external boiler, and a sealed system kit fitted to it, with the pump and the expansion vessel fitted inside the boiler cabnet.

The problem I have is that when I want hot water on its own, the radiators are getting warm. :?

The system is controled through 2 x 2 port danfoss valves. When Hot water is switched on, CH valve stays shut as it should, and the one for the hot water cylinder opens. I've felt around the pipes, and the central heating one is definately shut, and as far as I can tell it is not passing.

Could i be getting a back flow through the rads?????? What would cause this??? Should I have a non return valve of some description fitted in the system???

Any help or suggestions would be much apprieciated.
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Postby plastic_man77 » Wed Jul 13, 2011 10:51 am

@ kenny bush

When you say you fitted a heating system, do you mean you fitted the boiler & sealing kit yourself, or all the pipework, rads and cylinder as well, including wiring the programmer, (If not an RF type) and other electrical components (valves etc)?

If you only installed the boiler, did the system have the problem before you did any work or has it only occurred since?

There are ways to troubleshoot motorized valves, but something easy for you to do, with all due respect (and less complicated for me to explain), would be to drain your system, fit a compression isolation valve just before the CH motorized valve (If poss. If not, install it after the valve) and leave in the open position until you have re-filled your system and bled all the air.
Now, shut off the isolation valve and run your system on water only. If your rads don't heat up, it's the motorized vavle at fault in some way (mechanical or electrical) and if they do get warm, then you do have a reverse flow situation.

If the valve is faulty, if it's new, it will probably be down to your wiring. If it's old, get a new one and try that. If it still doesn't work, it's 99.9% your wiring.

If it's a reverse flow situation, I'd consider calling a heating engineer to help you out.
Alternatively, purchase the Wet Central Heating Troubleshooting guide from Corgi Direct and look up the Three T Rule (Or try and search for it online, but I've had little luck). It will help solve your reverse flow problem. Non-return Valves aren't normally designed in to a heating system from the off, they are put in afterward to correct poor pipework configurations. If you follow the Three T Rule, reverse flow will be eliminated naturally.
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Postby kenny bush » Sun Jul 17, 2011 8:58 pm

Hi, Thanks for the reply.

It's a complete new instalation. I'm not a plumber by any means, and a friend of a friend gave me a drawing of what to do. I completed all the plumbing work myself, and I'd consider myself fairly competant to do a job like this, and had a sparky friend do the wiring for me. I also had a plumber comision the boiler for me when it was completed. But I didn't notice the problem when he was here.

Both the motorised vaves are brand new, and I've pulled the lagging back from the pipes after the CH valve, and the pipe is stone cold.

I've looked up the 3 T rule, which I had no word of before, and I'm pretty sure that is safe to say that this is the problem. As most of the pipe work under the floor is plastic, it shouldn't be any problems to sort this out by moving some of the connections about.

I've just connected the cylinder return into the return from the rads, and then T'd a pipe into the rad return to go back to the boiler. By my reckoning, if I remove the cylinder return from the CH return, and then T it into the return from the boiler itself, and I'm guesing the closer to the boiler the better, then this will solve, or improve the problem, if it is a back flow issue.

Any thoughts on this would be apprieciated, as, as I mentioned earlier I'm only an engineer, not a plumber.

Also, is there any harm continueing to use the system the way it is for now? as I've got 2 broken wrists at the moment, so not really fit for working under the floor for a few weeks.

Thanks again for the reply, and poiting me in the right direction.

Kenny
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Postby plastic_man77 » Wed Jul 20, 2011 9:25 pm

@ kenny bush

There is no problem using your system as it is. No damage should be caused.

I have now found the 3 T rule online at:

Google "danfoss-randall.co.uk/PCMPDF/Introducing%20Controls.pdf"

As you are probably aware, this is a design feature associated with open vent systems, and your system is a sealed pressurised system, but apart from the position of the feed and vent, there isn't any harm in following the other good practises with the pipework.

Your boiler manual, section 4 fig.13, shows the above pipework arrangement while informing of the alternative positions for the expansion vessel.

Also, the bypass should be fitted immediately after the pump, (delivery side), and branch to the return pipework after the radiator and cylinder T's.

The pipework alterations you have mentioned sound like you are on the right track, but you don't need to get too close to the boiler with the cylinder return or bypass, the main concern is the order they are in on the return pipe.
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