Half diagnosed problem, how to fix and what info to give a pro Plumber

[motomob]

Like many people I have one of the dreaded pulsing showers once it is switched off. I read many posts here and elsewhere on the internet and came to the conclusion mine could be due to incorrect installation and or air trapped in the system.

So diagnosing, my shower is a mixer with a thermostat dial and single operation button. Pump is recessed & hidden behind a tiled wall in the shower so I have no idea what it is or how it is plumbed.
Fed by 1.5 year old combi boiler in the roof. One bathroom house, no other showers, no water tank.

Normal operation, set to middle temp, press button wait 20-40s depending on heating status and shower is at set temp. Time to achieve desired temp has no effect on pulsing. Flow of water does vary ever so slightly during this period but not vastly. Something others reported I saw in threads that during this period steam from the hot water feed can cause air pockets.
Switch off shower, immediate pulsing on the shower itself in the hose and on water pipes hidden under the floor and behind the walls. Now getting so bad I'm worried the pulsing is impacting their mountings. Pulsing can last up to 5 mins.

With my new found dangerous internet knowledge, I tried diagnosing. In the bathroom is a toilet and sink with separate hot and water taps. Before switching the shower on I opened the cold water tap to half flow. Switched on the shower and ran it for 1-2 minutes. Switched off and lo and behold no pulsing. Turned off cold water tap.

Tried test again but this time using the shower for 5-7 mins. Switched on cold water tap at quarter flow. Used shower for 5-7 mins, when shower stopped mild less pulsing than before was present. Whilst it was pulsing I opened the hot sink tap as well to half flow and the pulsing immediately stopped.

So my ask to the forum, is there enough information above to give the exact problem to a good local reputable plumber to work off? If so what kind of fix would he need to do based on this information. If there is a known fix for this behaviour, how much roughly am I looking to fix it. I'm not looking to do this myself just want to avoid multiple visits and hopefully fix in one go.

Thanks in advance for reading and any help.

 

[motomob]

Out of interest, can you test the shower on fully cold then fully hot and report?

Fully cold, 30-40s to reach pure cold temp, let run for 1 min, switch off, mild hammering for 2-3s then went away by itself.
Repeat for fully hot, same test, again mild hammering for 2-3s and went away by itself, no interaction needed to stop it.

Repeated a cold water test back to back with a cold test and the hammering is even less, maybe 1s max of hammering.
Same for hot test back to back so it does seem to be the mixing that is causing the air pockets and hammering? I guess if I could get the hot water temp down from the boiler somehow it might help or fix this which I thought the thermostat dial would do or is this just a faulty processor?

 

[Gasmk1]

Could you have a loose stop valve causing water hammer

 

[motomob]

Is the shower head dripping when it's not on?

Tbh sounds like you need a new processor. Replaced a few myself, they usually go after about 10 years, that one my friend looks like it's way past that age.

No consistent dripping. The shower head does always have a drop ready to drop though.

The age of the processor is 10+years. Found the manufacturing date, make that 2003! I think you may be right but just wanted to do as much amateur troubleshooting to make sure it is that before buying one and calling someone out to fit.

 

[motomob]

Could you have a loose stop valve causing water hammer

Good question. As far as I can see there are two in the kitchen and several on the boiler pipes but none seem loose.

Right now with the tests done I can only think it is a faulty processor (£££) due to the mixing but the fact there is still 2-3s of hammering even on pure cold or pure hot has me worried there is also a second fault like you mention a loose stop valve somewhere else I'm missing.

Time to call out a pro and supply the info and help you guys have given me. If it's a new processor it'll have to wait a while... but I will update the thread once they've been.

 

[Gasmk1]

Good question. As far as I can see there are two in the kitchen and several on the boiler pipes but none seem loose.

Right now with the tests done I can only think it is a faulty processor (£££) due to the mixing but the fact there is still 2-3s of hammering even on pure cold or pure hot has me worried there is also a second fault like you mention a loose stop valve somewhere else I'm missing.

Time to call out a pro and supply the info and help you guys have given me. If it's a new processor it'll have to wait a while... but I will update the thread once they've been.

you wouldn't be able to see its loose its the jumper inside that becomes loose

 

[motomob]

Hi all, once again thanks to everyone that replied. Problem resolved.

New Aqualisa A1 processor installed and no more shower hammering. Annoying it had to be the most expensive bit but glad I tried everyone's ideas first so I was 99% sure the replacement would fix it.