Megaflo unvented cylinder low hot water pressure into shower

[Mercenary Keyboard Warrior]

Is this built into the surface mounted unit itself, or separate parts built into the pipework feeding the unit? If the latter, then this pipework is behind a tiled wall and completely inaccessible.




Yeah its about the same, none of the taps flow great but I think its because they are mixer taps.

If its surface mounted its probably in that "box"
Its worth investigating that unit itself IMO.
Its likely the problem, as such you can probably see the pipework inside and work out how hard it is to mess with.

I had to replace a thermostat section on a built in in the past and it was a sealed unit, so cost me about £125 for a new one from the manufacturer. (Circa 20 years ago now).
I had two of the same shower in the house so swapped them over, proved it was that unit and swapped them back.
If you really suspect the shower in theory you may be able to disconnect the hot pipe, stick a hose or something on the end then turn the water back on, it will ofc come out of the hose at system pressure then. (obviously you would isolate the water and depressure before messing with the pipework)
There could well be some filters in the unit as well but I haven't come across any myself.

Do you have a model number for the shower?

 

[fezster]

Is this built into the surface mounted unit itself, or separate parts built into the pipework feeding the unit? If the latter, then this pipework is behind a tiled wall and completely inaccessible.




Yeah its about the same, none of the taps flow great but I think its because they are mixer taps.

The shower valve can be removed from the wall and will most likely have integral strainers on both inlets.

Although, as I asked above, do the taps have poor hot flow compared to cold, or is both hot and cold flow to the taps poor?

 

[fezster]

This was my thought, had the same years ago

BTW air bubble wont affect the flow, its there to soak up the pressure when the tank is heating, no bubble means no compression available to the expanding water.
If your missing the bubble the pressure relief will kick in on heating, and some water will vent down through the tundish

After a decent heating cycle check the tundish to see if any evidence of water. Or depending where it goes outside you may be able to just stick something like a mug underneath to test it.

Totally agree with this, although would also add that the air bubble acts like an expansion vessel and gives a (albeit short lived) accumulator like boost to the hot water when you first turn an outlet on. This means you will get greater flow for a short period of time.

 

[danlightbulb]

Do you have a model number for the shower?

It physically looks the same as this one but I don't know the exact model number. https://www.victorianplumbing.co.uk...vcGOoM3spL_dA6owblxoC82AQAvD_BwE&gclsrc=aw.ds

The shower valve can be removed from the wall and will most likely have integral strainers on both inlets.

Although, as I asked above, do the taps have poor hot flow compared to cold, or is both hot and cold flow to the taps poor?

All that comes out from the wall is two pipes, and the shower unit like the above just (by the looks of it) compression fits onto these tails. This is a combined shower/tap unit so the tap function has the same issue as the shower function.

The kitchen and bathroom sink taps are both mixer units, so are fairly low flow anyway. But as far as I can tell, whether on hot or cold the pressure/flow is similar.

The bath tap (combo thermostatic unit), if switched completely to cold, has a very powerful flow and pressure. It is when the hot water is introduced that the flow dies and pulstates.

 

[Mercenary Keyboard Warrior]

looks like it should be fairly easy to remove and test the flow to the pipe coming from the wall then.

We had some thermostatic mixer taps at work that behaved oddly and it was actually too much water flow of our very hot site water meant it heated up too quickly and then stopped the flow, very much like you describe, kind of pulsated and made all sorts of noises due to kind of hammering in the pipes (not water hammer as such)
fix was to lower the hot flow rate so it couldnt create such a high temp differential as quickly

 

[dlockers]

looks like it should be fairly easy to remove and test the flow to the pipe coming from the wall then.

We had some thermostatic mixer taps at work that behaved oddly and it was actually too much water flow of our very hot site water meant it heated up too quickly and then stopped the flow, very much like you describe, kind of pulsated and made all sorts of noises due to kind of hammering in the pipes (not water hammer as such)
fix was to lower the hot flow rate so it couldnt create such a high temp differential as quickly

You can test this pretty easily by turning the hot water tap partially off.


Have you messed with anything recently OP? Like switched the tap off? Could be you've opened it 'too much'.

 

[danlightbulb]

You can test this pretty easily by turning the hot water tap partially off.


Have you messed with anything recently OP? Like switched the tap off? Could be you've opened it 'too much'.

What tap do you mean? If you mean restricting the hot water flow from the cylinder, it can't be done - there is no valve on the inlet or outlet of the cylinder that doesn't also close off the cold water supply.

The only thing that my girlfriend says has happened in the last few months is that Severn Trent were working in the road (major diversion works going on in the area right now) and as a result of this the water supply was cut off on a few occasions over several months. She thinks the pressure is lower than it was before (but I think still adequate for the shower as the cold water flow on its own is strong).

We've not messed with the PRV on the inlet (if that's what it is).

Girlfriend is going to estimate the hot water temperature tonight using a basic thermometer held under the kitchen tap.

 

[dlockers]

What tap do you mean? If you mean restricting the hot water flow from the cylinder, it can't be done - there is no valve on the inlet or outlet of the cylinder that doesn't also close off the cold water supply.

The only thing that my girlfriend says has happened in the last few months is that Severn Trent were working in the road (major diversion works going on in the area right now) and as a result of this the water supply was cut off on a few occasions over several months. She thinks the pressure is lower than it was before (but I think still adequate for the shower as the cold water flow on its own is strong).

We've not messed with the PRV on the inlet (if that's what it is).

Girlfriend is going to estimate the hot water temperature tonight using a basic thermometer held under the kitchen tap.

It could be air locked? But highly unlikely unless she drained the hot water tank whilst the water was off?

You could try and put a wet and dry vacuum on the hot tap to suck through any air.

 

[danlightbulb]

I discounted an air lock as its a mains pressure system, and hot water flows from the other taps.

Maybe its just a faulty thermostatic shower unit. The only mechanical moving part on the whole system is the thermostatic shower valve.

 

[danlightbulb]

The issue was the shower inlet strainer/filter mesh on the hot supply inlet to the shower valve.

Was clogged up with greeny blue residue. Cleaned and reassembled, shower is back to full power.

I also removed what seems to be a flow restrictor/aerator in the bathroom sink tap which has improved things massively.

Was hard to tell what was going on when all taps were so poor flow. Bloody strainers and restrictors fitted no wonder things were poor.

Nothing wrong with cylinder at all.

 

[Hades]

We had this exact issue last year with low pressure in the shower. It turned out to be some kind of stuck valve in the airing cupboard next to the megaflow system. Sorry I can't be more specific but we have a British Gas contract and they just came and fixed it. The water pressure in the shower was like night and day afterwards.