New Boiler/cylinder etc. quote. Such complexity! Do I really need these gizmos?

[dweezil]

Not here. downstairs loo on mains direct and mains for bathroom wash-basin cold (mains cock off stops flow). Not sure about upstairs loo but pretty sure it's on mains as well. Thanks for explaining that possible scenario. However, the increased circulatory pressure on the c/htg pipes does concern me, though why there IS increased pressure when I'd thought this was governed by the pump, is beyond me.

You always used set the pressure manually on systems i've seen so as long as the boiler doesn't trip out with a low pressure alert you don't have to run a vast pressure or full mains pressure.

Had a panic call from our youngest last night as she'd accidentally over pressured her system, not leaks though.

The pressure drop across your pump will remain much the same but the whole system could run at a slightly higher pressure.

If you're worried about a very high mains pressure you can fit an adjustable regulator for about £40.

 

[notaclue]

Not here. downstairs loo on mains direct and mains for bathroom wash-basin cold (mains cock off stops flow). Not sure about upstairs loo but pretty sure it's on mains as well. Thanks for explaining that possible scenario. However, the increased circulatory pressure on the c/htg pipes does concern me, though why there IS increased pressure when I'd thought this was governed by the pump, is beyond me.

In your current setup, the little tank in the loft feeds your heating system (pipes and rads) so this system is only subjected to the low, gravity pressure of the water (which is why tanks have to be at the highest point). With a combi or system boiler, your loft tank gets removed and your heating is then connected to the mains supply and pressurised/sealed so the water flowing round it is now at a higher pressure.

E.g See https://forums.moneysavingexpert.com/discussion/4835680/new-combi-boiler-risks "weak joints, weak pipes & weak rads could all lead to leaks when changing to a sealed system"

You also have to consider your mains pressure for combi boiler flow. Will depend on the pressure of your water mains, which varies, not all locations/houses are the same. Some places will have very high mains pressure, some lower. Again, your plumber can advise.

 

[Mike Reed]

E.g See https://forums.moneysavingexpert.com/discussion/4835680/new-combi-boiler-risks "

Interesting read and the o.p.'s situation there resembles mine. Ta !

B.T.W., currently it's a gravity- fed system with 4 pipes into/out of the boiler but I gather the new heat only one will be 2 pipes only, which requires valves and other stuff we don't have currently. Can't see the drawback of a gravity system, with the caveat that our (very very old) bathroom rad is unpleasant on hot summer days. However, this only became a real hassle this summer. In a 'normal' British summer we hardly noticed the inconvenience.

Whereas boilers are guaranteed for up to 10 years with annual servicing, what are the guarantees on valves and other essential ancillaries? From my one experience of these (in a 2 zone installation), they can go wrong.

 

[Mike Reed]

If you're worried about a very high mains pressure you can fit an adjustable regulator for about £40.

I've no idea about my mains pressure. I turn a tap on and an adequate stream of water comes out. However, the loo cystern does fill up quickly and with attendant noise ! Am still puzzled by a system relying on mains pressure but governed by a (presumably fixed pressure) pump.

 

[dweezil]

I've no idea about my mains pressure. I turn a tap on and an adequate stream of water comes out. However, the loo cystern does fill up quickly and with attendant noise ! Am still puzzled by a system relying on mains pressure but governed by a (presumably fixed pressure) pump.

You're mixing up the two.

The whole system can be pressurised by the mains pressure but the pump in your house just ensures that the fluid runs from boiler through the rads etc.

You can adjust the pressure of your pump or set it to any constant pressure as required.

 

[Mike Reed]

You're mixing up the two.

Thanks for that, which I can understand as regards the boiler operation. However, what I can't understand is (sorry, bear with my ignorance), if a higher pressure in the c/htg pipes is commensurate with both combi and system boilers as opposed to an indirect system, why cannot the pump be set to lower that flow pressure, thus not potentially endangering old and/or varied piping?

 

[notaclue]

But the pipes will be subjected to increased mains pressure whether or not the pump is on or off. Think of connecting a hosepipe to your incoming water mains vs connecting a hosepipe to the bottom of your loft tank. The latter is under much lower pressure. And wouldn't be much use watering the garden, for example. A dodgy hose connector on the loft hosepipe might not leak whereas a dodgy connector on the mains water supply will because the pressure is much higher.

 

[Mike Reed]

Appreciated, notaclue; it's now dawning on me that the flow is mains pressure whether the pump is working or not. What I didn't understand was that the pipes are subjected to the pressure when the pump may be at the end of the system (as I think mine is so prob. the norm). Thanks for your tutorial patience

 

[dweezil]

Thanks for that, which I can understand as regards the boiler operation. However, what I can't understand is (sorry, bear with my ignorance), if a higher pressure in the c/htg pipes is commensurate with both combi and system boilers as opposed to an indirect system, why cannot the pump be set to lower that flow pressure, thus not potentially endangering old and/or varied piping?

To put some figures on it you'll get about 20 to 50 metres of pressure from your mains; imagine that as being the height to the top of the water in your local water tower.

The pump in your heating system will deliver something from 1 to 8 m pressure differential; typically i set to around 3 metres and see how it goes.

Atmospheric pressure is about 10 metres or 15psi.

You'll have a little dial on the boiler for pressure, something like 15 to 45 psi is the happy zone and it'll cut out if too low.

This helps prevent cavitation and keeps the system quiet, YMMV.

In an open system as we have here the tank in the loft determines the system pressure so in the bathroom we've got about 2m pressure. The shower pump is designed to work with 7 m negative pressure so it actually sucks the water from the tank if needed!

 

[hifinutt]

Had a vaillant eco tec pack up friday night at 21.40 . Called to see it sat am and refilled pressure but still no go . Gas engineer went out sun pm and thought it good be a pump or diverter

Contacted vaillant , took an hour of hassle with domestic and general who are the most incompetant company in the uk .however vaillant tried to sort this mess and had it fixed before midday on monday ...circuit board .

Cost 400 to fix altogether but cheaper than a new boiler !! Another BIG brownie point to vaillant