Boiler kettling, pump very hot, some pumping over.

[gr7]

I would be most grateful if somebody could give me an opinion on the following symptoms.

10 year old potterton boiler, with new style circuit board on an open vented system.

Once hot, the boiler kettles and then switches on and off every 2-3 minutes. Outlet pipe is very hot. Pump is also very hot.

There is some brown sludge in the f/e tank.

4 out of 7 rads are about a year old.

This has been a long term problem. Last year I ran the system with various chemicals and only ever got a marginal improvement (x400/x800). System currently has x100/x200 in.

My temptation is to change the pump next, but my rads all still heat up - so not sure if that would just be a waste of money!

Thanks!

 

[Armo74]

Some pictures of the pipework in the airing cupboard would help.
Cold feed maybe blocked,
maybe pumping over,
Is there a lot of air in the system?
Did you use the chemicals properly?
How did you add the chemicals?

 

[twgas]

Why were the rads replaced; asthetics, leaks etc?
System needs checking for correct instal/design, then, I would suspect a GOOD powerflush is what you need.

 

[gr7]

Thanks for your replys!

Rads in bedrooms and hallways were replaced due to aesthetics and TRVs were also fitted at sames time.

The chemicals were added (a year ago) via a drained f/e tank and then left in for about 2 weeks. This did produce a marginal improvement.

My bathroom rad, which is also connected to the hot water circuit, is old and needs a lot of bleeding - about a third full if air every week!

Thanks Gr7

 

[jackthom]

I'm not clear whether the radiators are getting nice and hot right down to the bottom or is the boiler cycling long before they have all fully warmed up?

 

[gr7]

Thanks for your reply.

The rads are all heating up nicely, even though boiler is kettling quite loudly and is cycling on/off every 2 to 3 minutes.

 

[Agile]

You would measure flow and return temps at the boiler whilst its still burning.

Tony

 

[gr7]

Tony, thanks for your reply.

I will be able to measure the temperatures on Wed with a pipe thermometer.

Just using my hands I can tell that there is a huge difference in temp, the water leaving the boiler is very hot!

 

[Agile]

The correct differential is about 11 C but the exact figure depends on the way its installed.

A seriously high figure would indicate a lack of flow.

I suggest you look at the site FAQ and remove the pump impeller. May be blocked with dirt.

While out test the torque with the finger test. See FAQ

Tony Glazier

 

[dominoman]

Are you 100% sure that the pump is actually spinning. I had a similar problem and the pump was getting extremely hot just because it was getting power but not turning. Turned out it was just stuck.

If your pump has a centre screw remove that with a screwdriver (I do it with the system running and the pump on). A little water will leak, but hopefully only a few drops. Put an empty ice cream container under just in case.

Then look through the hole to see if the pump is spinning. If not, waggle a screwdriver in there to try and release it.

With mine, once I'd got it started it freed up and was fine. Might be worth fitting a Magnaclean next time you can. That'll pick up any circulating magnetic crud

 

[Agile]

He says the rads still heat up so that implies the pump is turning! So does pumping over!

Consequently it seems like a blockage. Inspecting the impeller will indicate if that is blocked up. The finger test will show what the pump is doing.

The site FAQs are available to give full details of how to do simple checks and repairs all carefully written to be suitable for the less capable and taking into account many variants.

Tony

 

[First-time-buyer]

I am going to follow this thread. We have a open-vented system, which the boiler does heat only, with a in-direct loop in an immersion heater.

Our boiler does kettle, which we suspected it was limescale in the system, which a de-scaler was added. Its an old ideal mexico, which has a Temperature setting for the water, via a thermocouple. It cycles off and on depending on the water temp. we have attempted to balance the rads, as per the guide on here.

Flow can take up to 40mins for all the radiators to get hot, however warm within 10-15mins. Some radiators are new, and these get hot within minutes, whilst the others (old unfinned rads) take awhilst... nevermind the 15mm pipes that go through the concrete floor...

Some with the 9 radiators, 4 are piped via the concrete floor, and 5 are piped from above. Out of the 5 above, 2 are new and they get hot really quick. The remaining are slower, however these are old rads, no TRV and just an old skool lockshied. The solution might be to make the concrete pipes obsolete, run some 15mm surface from above...

So, instead of hi-jacking this thread, we plan to sit back and read the comments, and make you know that you are not alone here..

 

[Agile]

FTB needs to go and balance his own boilers instead of posting here!

Tony

 

[First-time-buyer]

Unfortunately i am at work...

Is that the answer that i need? Balance it...