Advice on combi boilers and mixer showers

paulloseby

We have a shower cabin with a mixer tap in. Until April we had a 35 year old Worcester combi boiler and everything worked fine. The boiler then packed in and we had to replace it with a Worcester-Bosch Greenstar 24i Junior Combi boiler. Now half way through having a shower, the water goes ice cold.
We asked the shower supplier and he said we needed a pressure equalising valve and so we bought one from him and had it fitted. It has made no difference.
We would really appreciate it if anyone has any ideas as to the reason and how to rectify the problem.
Many thanks in anticipation
Paul

nofoollikeold

With a combi boiler the cold and hot water pressures should be virtually the same, so I can't see the point of a pressure equalisation valve.

When the shower goes cold, does the boiler stop firing?

If not, then it might be the thermostatic cartridge in the shower (if it has one).

If the boiler does stop firing there may not be sufficient hot water flow to keep it going. This could be because the thermostatic valve in the shower is saying "enough hot" and cutting the flow. Try turning down the hot water temperature at the boiler and see if that helps.

southcoastrgi

the juniors are crap & a 24kw is the lowest output combi you can buy, but i tend to agree with above the flow rate isn't enough to keep the boiler running, try cleaning your shower head if the flow rate has got less

paulloseby

Very many thanks for your help on this. The shower is only a few months old but our boiler packed in at the end of March this year. We did have a 35 year old Worcester Heatslave G50 and when I spoke to Worcester-Bosch, they said we needed a 28CDi. Help-Link then came round and told us that we only needed the 24i Junior. The chap seemed to know what he was on about so we ordered one from him (but didn't use their payment package). Searching round earlier today, I find that the 24i Junior was actually discontinued that same month. I am wondering whether I was mis-sold to get rid of discontinued stock? I'm getting a Worcester-Bosch engineer to come and check it all now but this flow rate does seem to be the problem. Again very many thanks for your help. Regards Paul

paulloseby

PS - No thermostatic cartridge or controller - just one mixer tap

paulloseby

It turns out that although the company that sold us the shower told us to get a pressure equalising valve, once we had bought one from them and paid to have it fitted, they told us that it wouldn't make any difference. They did say to return it and they would give us a refund - but that means another £70 to have it taken out again. UUrrrggggg.

paulloseby

Many thanks for the help southcoastcgi and it does look like it is the flow rate. I don't suppose anyone has the specs of the 1980 Heatslave G40 Estate Combi that shows the flow rate do they?
Many thanks again everyone for your help
Regards
Paul

Alias_Omega

What about turning down the water temperature on the boiler, therefore the mixer shower will need to be "hotter", therefore more flow through the shower?


Bad Advice time - I had a similar problem on a ravenheat, I turned a knob on the 3-way valve inside.. Corgi probably knows what I mean...I would not advise this..

paulloseby

Hi Alias_Omega. Tried that. The settings are 1-6. On setting 4, after 3 minutes there was still only cold water. Same on setting 5. We turned it right up to just past 6 - the maximum and the shower stayed hot for just 2 minutes and 16 seconds and that was just on a gentle flow. I'm lost

paulloseby

Found the problem. Just spoken to the manager of Worcester-Bosch technical and it seems Help-Link sold us a 24i Jnr which is only really suitable for a 1 bed flat. We should have been sold a 34 or 38CDi Classic. The 24i is just not strong enough

thescouselander

That explanation makes no sense to me. Any combi should be capable to feeding a shower which, after all, is the same whether its in a flat or a house.

If you need more flow to keep the boiler going perhaps you just need to swap the shower head for a more free flowing one. Just as a diagnostic test what happens if you run the hot tap - will it run indefinitely or does that cut out too?