[Steve R]

Thanks a lot for replies. 

Will check but I'm pretty sure from memory that the hot cylinder feed and the the cold feed to the pump both come from the same header tank in the loft  (as per SamT's schematic) so both feeds to pump arrive at nominally the same pressure.  Which, as Sam says, is how it's supposed to be for this type of system. (Header tank also gives 'buffer reservoir' if your pump outstrips mains fill rate I guess)

Sorry should've mentioned the pump in question isn't exactly that specific pump I linked - just that style of unit but the troubleshooting advice from the manual is still relevant anyway, so thanks.

Is it  possible you can increase the pressure in the hot water system? Also does it tend to struggle when other systems in the house are using water, washing machine, dishwasher etc?

Well, raising the header tank and/or adjusting ballcock to let more water in must increase the pressure a bit....perhaps not significantly though if you're just gaining a few inches of head....Can't see any other way to increase hot water pressure though.
Strangely, I've had reports that when water is being used elsewhere downstairs in the house it can actually help to get the pump to come on.  This is counter-intuitive to me though - like you, I'd have guessed it would only struggle more.

"Flow rate" (rather than pressure) might be reduced through one side, if say the pipes take a long an convoluted route though narrower pipes 15mm as opposed to 22mm which I guess may cause an issue.

Could there be an issue with air locks in the pump, i.e. does the pump need bleeding of air, is there a mechanism for doing this?

As others have said, the flow switch might be dicky/gunked up. 

Thanks, less confused about the nature of the sensor/switch in the pump now.  Not sure why I'd assumed it'd be switched somehow by pressure sensors but it'll be flow rate sensor(s) as you and Jamie said.  Bit simpler.
Don't think there are any airlock issues - pump seems to run well and consistently as soon as it starts.

So, I think first thing to look at is any de-gunking possibilities at the pump, flow switch (hopefully get-at-able!), header tank and shower head.  (Tom - yes house is in beverley so rock hard limescaley water)
If that doesn't suficiently improve and remedy flow rate reliably, look at raising header tank level and see if that has any impact.

[SamT]

Well, raising the header tank and/or adjusting ballcock to let more water in must increase the pressure a bit....perhaps not significantly though if you're just gaining a few inches of head....Can't see any other way to increase hot water pressure though

1m height increase will give you 0.1 bar increase in pressure (1bar = ~10m head)

I assume that's probably not going to be possible and it'll be a right plumbing faff to extend all the pipe work. Especially in the confined spaces of the loft.

More I think about it, sounds like the flow switch to be honest.  i.e. the only way to get the pump to trigger is to massively increase the flow rate by either turning cold on full, or sucking like buggery.   Limescale may well be the issue.

Can you recall if it used to work fine, and has got steadily worse??

[tomtom]

Is this in E Yorks Steve or elsewhere? If it is then limescale might be the issue?

[webbo]

Beverley as stated in last but one paragraph.

[tomtom]

Beverley as stated in last but one paragraph.

My bad. Skipping posts... yes then - very hard water. Right up to the limits.

[Oldmanmatt]

Pressure switch would be my first instinct, given that it can be made to work by rapidly or greatly dropping the pressure by increasing either hot or cold flow.

Also, because experience has taught me to check the “On switch” first...

(Despite 30 years of being a Marine Engineer, I actually still forget).

[Steve R]

Had a quick look today. Thought I'd initially check what flow rate was like without power to the pump.  Quite surprised to find there was plenty of flow, both hot and cold - almost sufficient to shower without the pump running really, certainly more than enough to reliably bring the pump on when powered.  This, plus the intermittent nature of the problem, suggests it has to be a debris/blockage problem at either the pump or the shower tap?  The only other (unlikely?) way I can see flow being occasionally inhibited so badly would be if the pump was designed in a way that the impeller blades can sometimes come to rest in certain 'unlucky' positions; semi-blocking the pump exit until it got going a bit in a sort of pump catch 22.  Imagine these things don't have that sort of design flaw though so current best theory is bits of debris/limescale occaionally finding a configuration to all but block the flow.  I'm starting to suspect the porblem is centred in/around the shower tap - I think it was pretty cheap from Victoria Plum or similar, feels inconsistently stiff and crunchy to turn and generally a bit buggered... relatively easy fix if it is just that so will focus efforts there initially.

Thanks a lot for the tips, they've definitely helped. 

[Probes]

This is a little above the average diy job but I feel ukb knowledge may come to my rescue. I'm building a wide toe raft foundation (https://heatonmanufacturing.co.uk/raft-foundations-uses-types-cost/) for a double skin double garage with big loft. Doing a raft as the back of it is next to big drop (10 foot virtually straight down to a stream) and the ground is a little soft. All is good and I'm  confident in this logic.. but we had a minor f up whilst digging and the back toe is about a foot/foot and half deeper. So this puts the back at 3 foot and front less than 2. As the trenches are also sloped inwards I reckon there will be double the amount of concrete at the back compared to front. I'm concerned this will put foundation and building unevenly balanced. Does anyone have any experience with such structural shenanigans?   

[jshaw]

I think this post is best placed here... feel free to move it if not.

I'm looking to cut a retired rope to make a TRX / Rings set up from a tree in the garden.

I'm pretty keen to not cock up the cutting of the rope bit:

I plan to wrap the rope in climbing tape at the position I intend to cut, cut it with a sharp knife (Read: my partner's best cooking knife  ), remove the climbing tape then seal the ends with a lighter or over the hob if aforementioned partner hasn't found out about the use of the knife.

Does that sound about right? Is there anything else I should be aware of that would be easy to cock up?

[dunnyg]

I've always cut rope by heating up a knife and cutting by melting through it.

[Will Hunt]

I've always cut rope by heating up a knife and cutting by melting through it.

 

Use your oldest, crappest knife, because it's going to look like shit afterwards and you won't want to use it on food again.

[SA Chris]

Sharper the better, I use a stanley knife with a fresh blade. Cut down on a piece of wood rather than fold in half and cut in the air (if that makes sense) as if you do you can pull strands out the core that haven't been cut. Use a lighter outdoors rather than hob, smell is pretty foul and can linger, and you could drop blobs of melted plastic. You might need to squeeze burnt ends together to get them to stick, if you do this, expect to burn fingertips if you aren't careful.

[jshaw]

Seems like you've all saved me from getting in a unseen shitstorm of trouble. Many thanks!

UKB Hive Mind wins again. 

[UnkArl]

We’ve just done a big refurb of our bathroom, all the plumbing is new. Just fitted a new basin and tap but every morning and bed time (or anytime the tap hasn’t been used for a good few hours) the water runs a sport of slight orange/brown colour. I’m suspecting the tap, but anyone got any other ideas? Or if it is the tap solutions of how to stop it happening?

[tomtom]

If it’s the tap I’d have thought it would only be discoloured for the first half a second or so... anything else would reflect water in the pipes?

Are you in a hard or soft water area?

[SA Chris]

Hot, cold or both?

[UnkArl]

Sorry, should have said: it’s a mixer tap so difficult to tell (as there’s already water in the tap) and the discolouration only last a second, maybe two. We’re apparently in a “soft to moderately hard water” area

[tomtom]

Just goop inside the pipes I recon. Run it through for 10-20 secs before using. Should clean up. In hard water areas after a while a teeny layer of scale builds inside pipes that stops any of that too.

[UnkArl]

It’s been in about a week, so we have run the tap, and I gave it another good run earlier but it’s still happening. It’s weird because all the plumbing in the bathroom is brand new so there shouldn’t be any goop in the pipes, that’s why I’m thinking it must be the tap 
The basin is also “downstream” of a brand new shower (which we fitted about a month ago) and the toilet and there’s been no issues with those.

(Thanks for the help/ideas though)

[tomtom]

Yeah - weird.

I worked with a prof of water quality once - and he would always run his taps for 30 secs to one min before using them!

[UnkArl]

That’s a little concerning 

[tomtom]

Prob overkill (lead pipe concerns) but if you don’t visit your house or use your water for a few days it’s probably sensible just so you get fresh stuff coming through from the mains etc..

[Paul B]

Is it just that one tap in your household?

Turbidity issues can come from the wider network for a variety of reasons (incorrect connections  , work upstream, deterioration of the pipes themselves etc). Sheffield University worked on a project called PODDS that predicts such issues.

[UnkArl]

All the plumbing in the house is new (we had central heating installed when we bought the house last summer and also moved the kitchen sink, and now we’ve just re-done the bathroom).

Never noticed any discolouration issues until I installed the bathroom basin and tap about 2 weeks ago.

[remus]

My trusty £30 angle grinder has bitten the dust. Replacement options are

£40 bargain bucket jobbie
£60 slightly less cheapo option
£120 cordless deluxe version

The previous one died trying to wirebrush some some thick paint off a cast iron bench so whatever I go for it'd need to finish that off without dying. Leaning towards the mid-range option for that reason.

Is there any advantage to going with a cordless one? I've got some bosch batteries already so it's kind of tempting, but it seems a big premium to pay and I've never felt the need for a cordless grinder. Perhaps I just don't know what Im missing out on though?