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Normally described on boilers as an irregular rapid knocking noise. Usually caused by calcium deposits within the main heat exchanger. Most common on older boilers with cast iron heat exchangers. Usually easy to cure with the right chemicals and a little experience.

I do not recommend that as it can get forgotten and complicate anyone coming to deal with it correctly. But it does work for anyone without a compressor. But then I always carry a compressor with me. In practice boiler PRVs rarely get checked. But they are pretty reliable and usually do...

I would use hydrochloric acid at about 7% for cleaning plates. Usually using two applications of the acid. Sometimes warming it up to about 30 C and particularly moving it around quite a lot.

My way of thinking is that it is likely to be an electrolytic action. This can often be caused by faulty wiring causing currents in earth wires. My first check would be with a clamp on ammeter on earth connections around the plumbing.

Alls well that ends well! But I don't understand your original reluctance to go and have a look in the loft. Nasty cold dark places I know but all the evidence pointed to a problem up there!

When cold what is the depth of water in the header tank? Only needs to be about 100 mm. But when hot expansion increases that to about 200mm.

I used to like the Screwfix Kudox rads which are made in Turkey and seemed quite solid.

You would need to see if the diverter valve is moving when the hot water tap is turned on.

It is serious from the boiler's point of view. If the PRV was operating then the system pressure would probably fall below the minimum needed on start and stop the boiler from starting up. In reality the EXV { expansion vessel } probably only needs a few strokes of a foot pump to add a...

I would expect any competent service engineer to ask questions about the pressure to see if it needs further investigation.

Unfortunately there are a lot of different views on what to do on a service. As a minimum remove the cover inspect carefully inside for leaks or other problems, Check the burner pressure or gas consumption. That might take 30 minutes on site so £60 to £90 perhaps. These things are slewed by...

For myself I would make it very simple with just one connection at the effective furthest HW point from the cylinder. I would also time it and use a thermostat to turn off the pump when the return from it became just warm.

And so did I. But it was after being on secondment from the BBC to Qatar Television that I decided to drive back to the UK from Doha. I allowed 30 days although some people driving long hours did it in just 10 days. I made it into a holiday and took about 14 days.

Most secondary returns are just done in 15mm as it only needs to be able to create a small flow to keep the hot water circulating a very small amount. Obviously quite a lot of lagging is required on the hot water pipes which is something which is not always done in this country. Just as a...

Government policies and gas supplies may be quite unstable over the next few years. So my strong advice would be to keep the existing for a few years and avoid wasting money buying something which may not be the best solution in a few years time.

If it was my property then I would wish to place pipes under the lagging to reduce the chance of freezing up.

Stop cocks need to be exercised every three months to avoid any risk ofetting jammed when needed in the event of a serious leak. In addition the gland nut needs to be kept very slightly tight to avoid the packing leaking as yours is doing.

Well in theory it might as I mentioned in my third paragraph. However the flow temperatures for modern condensing boilers is usually set at 70 C and hot water for 55C to 60C so I do not see much serious scope for a very excessive over temperature. For the ABV to open under normal CH...

Yes thats the usual correct position to fit it. But if it was for me then I might fit it across the two port for the HW cylinder so that if it did operate the heat could be stored in the cylinder. But pedantics might claim that in a fault condition the hot water might exceed its temperature as...

An auto bypass valve is needed when a situation can arise that there is no flow from the pump. That might happen when there are two or more two port valves. But a three port valve always has at least one port open . So an auto bypass valve is not required.