No pressure or DHW on Baxi Instant 105e

[HellTel]

Hi guys
Well we've had this problem for months now, we don't have two pennies to rub together so we've put up with it but hopefully I can progress it now and I can have a crack at fixing it......

We have a Baxi Instant 105e that won't keep any pressure, we have to top it up literally every few hours. The discharge pipe constantly drips when the heating is on and every now and then it purges and a lot of water comes out of it (the pressure is much less than 3 bar when that happens). Is this likely to be the Pressure Relief Valve at fault?

Also, we have no DHW on demand. Well, that's not strictly true, we can get the contents of the Expansion Vessel out but that's it. When I turn a hot tap on, the boiler doesn't fire up. If I remove the microswitch on the front of the Diverter Valve Assembly and press it, the boiler fires up and the DHW LED comes on. With the switch still disconnected, I can see the pin doesn't come out when I turn a hot tap on. However, if it's time for it to top up the preheat then I can see the pin come out automatically.

Thanks for any light you can shed, I'll really appreciate it.
Just ask for any more info needed.

Terry

 

[gas4you]

I would start with the basics of replacing the prv and the DHW diaphragm.

I would also suggest you check the EV pressure.

See FAQ's on how to do this.

 

[HellTel]

Hi
Thanks for the response, I'll try the PRV for the pressure problem.

Like a putz, I forgot to say something on my post. When the preheat fires and the DHW LED comes on it's the CH valve pushrod that pops out, the DHW pushrod doesn't budge. When I depress the DHW microswitch, the DHW LED comes on, the boiler fires but but still no hot water from the tap.
Does that change your opinion on trying the DHW diaphragm?

Thanks
Terry

 

[mario500]

A new diaphram is needed as previous poster says. The symptoms describe confirm that. You should be able to get both parts for less than thirty quid and both are easy to change on that model. - but you may find that your expansion vessel has gone also - to test that you need to undo the cap and press the valve in - if you get a load of water out of it then its kapput. a little whisp of water is ok but not a constant amount.

Good luck fella


Al

 

[HellTel]

Thanks for the info. I've found a supplier of the parts and checked out how to fit them, looks like no worries there (famous last words!). Having looked around, I really, really hope that the Expansion Vessel isn't knackered as it looks like that'll be out of my hands with the whole boiler having to be removed from the wall!

 

[gas4you]

The ch pin will always 'pop out' as this is used to prove the pump/flow through the boiler

 

[ChrisR]

I really, really hope that the Expansion Vessel isn't knackered as it looks like that'll be out of my hands with the whole boiler having to be removed from the wall!

Nah, you can leave it there, and put a much cheaper one somewhere on the pipework, return side preferably. 8 litres should be enough. They come in various shapes (see faq). Under £30 inc fittings.

 

[gas4you]

Chris, as this is the instant, do you know if a knackered EV and an external one fitted will affect the pre-heat?

I have wondered about this but have never found an exact answer yet

 

[ChrisR]

It works, you get more preheated water! You ARE relying on the tyre valve cap thing to hold your 3 bar in though. They seem to be OK but...

 

[HellTel]

Well that's great. I hope I don't have to do it of course but if I do then that looks cool. More preheated water would be great too as it's never quite enough to last until the on demand water gets to the tap.
I'll keep you posted how I get on (just in case you might be interested )

 

[HellTel]

Just tested the EV, when I pushed the pin in on the valve air came out so I'll take that as a good sign and keep my fingers crossed

PRV and diaphragm ordered and cheaper than even I hoped, only just over £17 inc delivery so like I say, I'll let you know how I get on....

 

[BigBurner]

It works, you get more preheated water! You ARE relying on the tyre valve cap thing to hold your 3 bar in though. They seem to be OK but...

You will only get more preheated water as all the vessel will be filled with water instead of air and water. But!!!! if the diaphragm is holed water will get to the other side of it and be heated, but will not get back out through the hole fast enough, if at all, so not so much pre-heat. The diaphragm is in there holed and flapping. Also relying on a shrader valve to hold the water pressure is wrong. It was designed to hold air not water.

If the internal vessel's diaphragm is holed it must be replaced.

 

[HellTel]

Just an update for you as I promised I would.
I have fitted the diaphragm and PRV and I now have lovely hot water on demand and the boiler is keeping pressure, hooray!

So thanks very much for your input guys, I'm very grateful!

Cheers
Terry