I Have very little hot water up stairs. I have a sime super 90 boiler and have had it for 10 years it has worked well for most of that time but recently we have noticed that when running a bath the water would be hot for a while and then go cold. Downstairs the water was hot, the
problem only seemed to be when running a bath upstairs. Now we have no hot water at all
The central heating seems to be ok. We have very little money, what do you think the solution could be?

Christopher Nembhard, November 2005

I have sime 90 super plus the heat comes on but no hot water. Tried with heating on still no hot water. Never happened before. Can you help me. Zaf

zaff, February 2017

Further to my previous answer the diaphragm has gone again in my Sime Super 90. Early signs of this are poor hot water when CH not in use; radiators heating up when running hot water; air in hot taps/pipes.
Easy fix - £10 for diaphragm and washer kit off eBay - as I said before easier to remove divertor valve from boiler (instructions to do this can be Googled), although you do need to be a good DIYer to do this yourself, a competent plumber should manage this in a couple of hours.

Chris H, December 2012

I have a sime super 90 it has had this prolem 3 times now. You can buy a replacement diaphram for less than £1.50 but they are very difficult to fit because of the position of the diverter valve. It would be both quicker and easier to remove the valve and then either fit a complete new valve (costing £50-80.00) or replace the diaphram for £1.50. One word of warning though once you change the diaphram only expect 2-3 years use out of it.

Chris H, January 2009

Problem sounds like you diverter valve is faulty You can fit a service kit for about £25 but it most likley be the one at the top under the 8 screws {perished or hole}If I remember right they are about £15 the new valve will cst about £50 but these are all straight forward to change hope this helps If you want to no how to change one email me on maked@talktalk.net

Kevan Davison, January 2008

I had the exact same problem with my Boiler, the problem is the
divertor valve (which diverts hot water into the heat exchanger away from radiator circuit) which then in turn heats the mains water passing through it.A divertor valve is around
£50 but the main fault could be repaired by either of the following depending on further investigation.(approx £ 100 fitted)(if you are not going to fix this will help estimate cost so you don’t get ripped off when they say you have to buy a new valve)
NOTE –for some ‘qualified’ plumbers it may be cheaper/quicker to let them change the lot
As they should really be working in a call centre!!
The divertor is a brass casting with several water pipes coming out of it with a circular brass cover which has around ten 10 to 12 screws holding it on(picture available on google images)
(Giannoni diverter on SIME combi,s)
(your plumber/ gas engineer(in UK) needs to carry out the following straight forward steps)

On top of the diverter valve is a black box, get someone to turn on the hot tap & listen for the clicking of the microswitch, if it does not click remove the top half of the black cover(isolate electricity first) if you swivel the black box so you can view the back, you will see a metal pin with a round flat plastic plate on its about the size of a old ½ pence piece(decimal)this is underneath a microswitch .Try the hot tap again whilst watching to see if the metal pin with plate on it move enough to make the switch click, ie presses it.
If you then check the switch (in situ) by pressing momentarilly the switch with a insulated implement (don’t dislodge the plastic plate on the pin,which could get lost in the boiler pipework) If you hear the boiler ignite then the switch is fine if it does not remove the switch & take it to Maplin electronics /RS components for a replacement which is roughly wait for it
£1.30.
If the boiler did light when switch operated then the problem is usually the Diaphragm (ie Diaphragm is not pushing microswitch because it is punctured.(giannoni Diapragm picture on Google for SIME usually)(boiler must be lighted & electricity on for test) The diaphragm is inside the diverter valve under the cover held on with 10 to 12 screws.This requires you to drain the system first & turn off water supply.If there is adequate clearance you may be able to leave the valve in place whilst you unscrew top (may require cranked screwdriver)(if you do remove valve ensure you have replacement fibre washers for reassembly)
First remove the microswitch assembly which is held with a circlip in a groove in the div valve body around where the plunger rises & falls.(don’t drop circlip) lever out with a screwdriver on the tab at the back or pull the tab with long nose pliers.then lift microswitch off the plunger (no need to unplug wires) .
Now you can remove the lid by undoing the 10 screws (have old rags etc ready to catch water residue).lift off lid carefully, inside attached to the metal pin/plunger is a round black rubber diaphragm with springs etc attached (note where large loose spring is fitted for reassembly) now remove rubber diaphragm complete (just pulls out) with metal shaft.
Check for holes if it is damaged take it to a plumbers merchants/ or order online etc you will need diverter valve brand etc there you buy a diaphragm kit for £10- £20 .(also check the brass mesh in the water inlet is not blocked with silt, )Then reassemble & ensure that when re presurrised with no leaks that when the hot tap is on the micro switch is pushed by the plunger which in turn lights the boiler main burner.

Note most people should not attempt this unless they are mechanically minded & don’t work in a call centre etc as serious injury could result(explosion etc) if you disassemble the wrong parts ie gas valve etc or you could end up with a bigger bill if a dishonest emergency plumber is called when you get stuck or end up with no water or worse still could lead to serious deafness caused by your other half .

NOTE 2 If you work in a call centre & fix the above problem yourself get on a gas plumbers training course straight away !

RS, March 2006

Hi Chris, this is not actually an answer to your question but another question, i have a Sime super 120 (similar to yours) and the same problem, tried to contact Sime Uk but no luck, have u sorted out the problem with your boiler? If so can u please tell me how to fix mine?
Thanks
Nik
msflsim@gmail.com

NiK Kovacevic, December 2005