Old boiler with new behaviour - what do I look for?

[Itsallgood]

Hi All,

I've recently noticed that my upstairs rads get quite warm even when the heating is turned off but when the hot water is turned on.

A bit of research tells me that this is likely to be a sticky check valve in the radiator circuit.

The system is quite old but works very well normally, hot water is gravity fed, no two-way valve at all and the rads employ a Grundfoss pump for circulation. The boiler is an Ideal Concord W WRS 255A which I'm guessing is around 30 years old.

I had a gas fitter out to quote me for a replacement boiler about 2yrs ago and he quoted me a large figure but said "to be honest mate it'll probably last for another 30 years so it's not really necessary", so I didn't bother.

So my question is what would I be looking for and where when trying to locate this 'check valve'? - would it be inside the boiler casing behind the flap that covers the controls and pump? What would it look like?

I'm wondering if giving it a gentle tap might free it up inside, otherwise I guess will need to drain down and replace it.

 

[gavgas]

Hi, you probably don't have a check valve. With a gravity system, heat rises and causes hot water to flow from the boiler up to your cylinder, around your cylinder coil, then back down to the boiler. There are two pipes for this, usually 28mm coming out of the boiler, no pump and no valves, your feed and vent pipe usually connect to this circuit.

Your radiators both up and down stairs are fed from another two pipes at the boiler, flow and return. There is a pump on the return which is controlled by your room thermostat and timer. The problem is that when your timer is in hot water only mode, the boiler comes on, gravity and heat then cause a certain amount of flow through the upstairs radiators even though the pipes feeding them are significantly smaller than the cylinder ones.

The most sensible option is to just turn those radiators off in the summer or fit TRVs which will do the job for you automatically. Another option is to put in a 28mm motorised valve and cylinder stat and turn it into a C plan, but that does require a bit of work, draining down etc and is not really necessary. You could put in a cylinder stat and use it as a changeover switch to give you a bit more control over the hot water temperature. This will prevent the boiler cycling and keeping itself warm but does require a bit of wiring.

Gavin

 

[Itsallgood]

Hi Gavgas - thanks for the reply, much appreciated...

Your synopsis of my crotchety old system seems to be correct, the only thing being that this latest development where the upstairs rads heat up when they shoudn't has never happened before.

I'm at a loss as to why this is suddenly happening and a bit concerned that in the the height of summer it will be unbearable with the additional unnecessary radiator heat, aside from the wasted energy.

What could possibly have changed or gone wrong?

Thanks again for reply,
Tony

 

[St0rmer66]

A check valve on the flow to the heating circuit will stop this. The pump is strong enough to open it but the gravity heat is not. Just make sure you fit it in the correct direction .

 

[gavgas]

make sure you haven't left the immersion heater on, if you have, the temperature difference between the boiler and cylinder is lower than usual. This can cause the velocity of water through the cylinder coil to slow down as the return temperature is higher. Because that slows down, the heat input to the water has to somewhere so it can start circulating through the radiators.

Another thing to check is the boiler temperature setting, if that's been increased the same thing can occur as more heat has to transfer into the water.

A build up of sludge can also cause these symptoms in the water circuit as it's velocity is slower than that of the radiators although that usually manifests itself as the hot water no longer heats and the boiler cuts out quicker than usual

hope this helps

Gavin