Hot /cold/hot/cold etcetc... help !!

[dalebear]

hi there..
i had to get a plumber in to fix my shower going hot then cold, hot then cold every 5 seconds or so. He advised that my boiler was okay, a Worcester 24cdi, so the Mira shower should be replaced, so we`ve just done that, costing us £400...
guess what...the shower is STILL going hot then cold..as well as our taps.
can anyone help, so i can tell him whats wrong when he eventually answers my calls !
many thanks
Jim (becoming skint very quickly)

 

[xr4x4]

What does the boiler do when you run the hot tap?

It should fire up and continue to run while the tap is opened, or does it cut in and out...

 

[dalebear]

Hi there Paul..it cuts off, then back on,them off again,, etc.....
have you sen this before, or is it quite common ?
Jim

 

[mickyg]

probably plate heat exchanger on your boiler.

 

[Whitespirit66]

What model Mira shower was it. For that price, sounds like a Combiforce or similar.

Looks like he's diagnosed it wrong anyway, but surprised he didn't replace the shower's cartridge.

 

[dalebear]

Hi Guys...Is the plate able to be replaced ? are they expensive ?
and the shower is now a Mira Ordo..220 for the shower, 105 for fitting and the rest for the tiler to fix the tiles the plumber burst ( i had some spare thankfully)
JIm

 

[dalebear]

as for the cartridge, he said it would be just as cheap to replace the shower.. if only i wasnt as hasty and did a bit of research first. we`ve got friends over from Ireland at the moment, then americans next month..so was in a hurry to get it fixed....
.you guys are brill !

 

[Charnwood]

What does the boiler do when you run the hot tap?

Hi there Paul..it cuts off, then back on,them off again,, etc.....

And the plumber recommended changing the shower?!?!
Get him back and hammer it out with him - massive discount to get it fixed properly!

 

[dalebear]

Thats what i want to do !! Just need to be 100% sure that its the heat exchanger now. Do you know if thrres anything else i can do to make sure that it is ? Jim

 

[xr4x4]

I'm afraid I don't know enough about this boiler to know and would need to be there anyway.

Hot water problems on combis are normally, flow switch, diaphragm or Heat plate exchanger.

Has the flow been reduced from the hot tap over time?

I would suggest you get a 'boiler engineer' in to look at it. Ask them over the phone if they know of your boiler and if this a common fault.

 

[dalebear]

Hi Paul..
when the water started to go hot/cold in the middle of the colder weather, the plumber adjusted an inlet pipe to slow down the flow,and said that the water wasnt getting enough time going through the boiler to heat up, therefore it was running hot/cold....after adjusting it, the pressure was much lower from the taps, and the shower did indeed feel like it was retaining a warm heat, but certainly not hot !.
There`s a heating engineer not too far from me, and i`ll ask around what he`s like before i ask him to nip in for a wee look.. thats another thing i`ve learned now...
anyway, thanks again to you and the guys for helping me along with this...i`ll keep you posted as to the outcome....
Best regards
Jim

 

[dalebear]

Hi Paul...me again!
do you have a Sierra XR4x4 then ?
jim

 

[MJN]

It could well be a perished diverted diaphragm; a very common failure mode on these boilers.

The easiest way to diagnose it without going near the boiler is to have a hot water tap open whilst the shower is on. This will maintain a high flow through the boiler which, with a gradually failing diaphragm, will be sufficient to keep the HW demand requirement on. It's little good as a permanent workaround given the resulting poor HW flow to the shower but it'll help pinpoint the blame on the diaphragm if the hot-cold-hot-cold symptoms disappear.

Mathew

 

[dalebear]

Hi again..
Just tried the hot tap running at the same time as the shower and they are both going cold the warm etc etc about every 10 seconds...jim

 

[MJN]

Ah okay, chances are it's not a failing diaphragm then.

When the water is going hot-cold-hot-cold is the hot water demand light (tap symbol) on the boiler going on and off, or constantly on? I should've said earlier, if it's the former then that can point to the diaphragm also.

Mathew